Viacom has overhauled the management of its cable groups, with Doug Herzog adding oversight of MTV, VH1 and other networks to his portfolio while TV Land and CMT move into the kids and family group headed by Nickelodeon chief Cyma Zarghami.

The restructuring comes after the exits this week of longtime MTV Networks exec Van Toffler and TV Land president Larry Jones. Viacom is under increasing pressure to turn around the declining ratings at its flagship cablers, which has led to turbulence in its affiliation negotiations with some MVPDs. News last week of Jon Stewart’s pending departure from Comedy Central’s “The Daily Show” didn’t help matters.

“Our industry is in transition, and change does not always come easy, but we have a tremendous amount of talent at Viacom, and we are innovating at every level and at every brand,” Viacom CEO Philippe Dauman wrote in a memo to staffers Thursday. “We are working hard to adapt to changing audience behavior, to incorporate new forms of distribution and to better integrate technology into everything we do.”

In the restructuring, Herzog and Zarghami are divvying up the cablers previously overseen by Toffler, who will remain on board through mid-April to help in the transition.

Herzog is a Viacom cable vet who will head the Viacom Music and Entertainment Group, comprised of Comedy Central, MTV, MTV 2, VH1, Spike, Logo and related digital networks. Zarghami, who is close to hitting her 30-year anniversary with Nickelodeon, will lead the expanded Viacom Kids and Family Group, housing Nickelodeon and its offshoots, and adding TV Land, CMT and CMT Pure Country.

In the restructuring laid out by Dauman, Herzog and Zarghami report directly to him, as does Paramount Pictures chairman Brad Grey, BET Networks chief Debra Lee and Bob Bakish, president of Viacom Intl. Media Networks.

Herzog had previously headed a cluster dubbed Viacom Entertainment Group, which consisted of Comedy Central, Spike TV and TV Land. He came up the ranks at MTV starting in 1984, and then lead Comedy Central during its mid-1990s growth spurt that saw the launch of “Daily Show” and “South Park.” He left the Viacom fold from 1998 through 2004 when he headed entertainment for Fox Broadcasting and USA Network.

After Toffler announced his resignation Tuesday, there was some speculation that Dauman might look to bring in new blood to send a message to Wall Street that he is shaking up the status quo. But such a move might have caused more disruption inside the company, which is known for the longevity of execs like Herzog and Zarghami.

Here is the memo from Dauman:

Dear Colleagues,

In the nearly 30 years I have been fortunate to be associated with Viacom, we have always been a leading force in our industry, through our breakthrough programming, through our creative innovation and most of all through our ability to continually reinvent ourselves.

Today, we are announcing changes in three of our domestic network groups, creating two new organizations built around proven leaders with great creative track records. Doug Herzog, will lead the newly formulated Viacom Music and Entertainment Group, and Cyma Zarghami, will lead the expanded Viacom Kids and Family Group. The new groups are an enormous opportunity for us to take advantage of our strong creative teams, to share our expertise, and to promote greater cross marketing and, in some cases, cross channel programming activity.

· The Viacom Music and Entertainment Group will consist of MTV, MTV2, LOGO, VH1, Comedy Central and Spike, as well as the related digital networks and MTV’s “Always On,” which fuses the immediacy of social conversation with the power of television. MTV, VH1 and LOGO are among the most iconic and engaging brands in our industry, and thanks to Van ‘s long-term and stable leadership, they have top teams who will no doubt make this a seamless transition.

The Music and Entertainment Group will house a portfolio of popular programs, ranging from Teen Wolf and the VMAs on MTV and Guy Code on MTV2; to Bar Rescue and Ink Master on Spike; to Love & Hip Hop on VH1; to Broad City, Key & Peele and South Park on Comedy Central; to RuPaul’s Drag Race on LOGO.

The role is in part a coming home for Doug, who joined MTV in 1984 and rose to become President of MTV Productions, and later, President of Comedy Central, where among his notable accomplishments, he launched The Daily Show and South Park. Before rejoining Viacom in 2004, Doug served as President of USA Network and also President of Entertainment for FOX Broadcasting Company. Doug has a proven ability to move seamlessly between the business and creative worlds. He understands what it takes to stay relevant and on the leading edge of popular culture, and under his leadership, Comedy Central, Spike and TV Land have established distinctive programming voices in the entertainment landscape. Doug will continue to be based in Los Angeles and New York.

The Viacom Kids and Family Group will comprise all the brands currently in the Nickelodeon Group, including Nickelodeon, Nick Jr., TeenNick, Nick at Nite, NickMom and NickToons, as well as TV Land, CMT and CMT Pure Country.

TV Land, which originated in this group, and features classic shows and new originals such as Younger, and CMT, which appeals to heartland audiences and includes major events like the CMT Music Awards, have talented teams and established brand presence. Both will benefit from the expanded group’s leadership in family programming that includes iconic live action and animated Nickelodeon, Nick Jr. and TeenNick programs like SpongeBob SquarePants, Dora the Explorer and Nickelodeon’s Kids’ Choice Awards.

Cyma, who will celebrate 30 years with Nickelodeon this year, has a long history and formidable track record as a creative programmer and successful executive. She is an insightful and extremely capable leader and has grown Nickelodeon and its sibling networks into brands that are beloved by kids and families around the world. The successful Teenage Mutant Ninja Turtles franchise is just one example of her ability to reimagine properties and take them to new heights. Cyma joined Nickelodeon in 1985, was named general manager of Nickelodeon in 1996 and became Group President in 2006.

Doug and Cyma, along with Debi Lee at BET Networks, Bob Bakish at Viacom International Media Networks and Brad Grey at Paramount Pictures, will continue to report to me. TV Land will move to the Viacom Kids and Family Group immediately, and the other networks will transition between now and Van’s departure in mid-April. More information on the specific organizational changes will come from the Group leaders in the coming weeks.

Our industry is in transition and change does not always come easy, but we have a tremendous amount of talent at Viacom and we are innovating at every level and at every brand. We are working hard to adapt to changing audience behavior, to incorporate new forms of distribution and to better integrate technology into everything we do. That includes our expanded data and research capabilities; our multi-platform, multi-distributor approach; our groundbreaking advertising sales units, Velocity and Echo; and our new central hub for digital research and development, The Viacom Lab. Just to name a few.

I have great confidence that by working together to embrace the changing landscape and by continuing to bring our best creative work to audiences — we will succeed. Thank you for your continued dedication and hard work. I know you join me in congratulating Doug and Cyma on their new responsibilities.

Warm regards,