As I reported earlier today, social gaming giant Zynga has posted another filing with the Securities and Exchange Commission.

That includes Chief Business Officer Owen Van Natta stepping out of an operational role and forfeiting shares in the process. To be exact: That will be 4.6 million options and close to 800,000 restricted stock units.

All of the details are in his transition letter in Zynga’s massive new S-1, which is in exhibit 10.12 to the amendment filing.

I would start at page 119, but to summarize: Van Natta is keeping all the vested stock options and restricted stock units, currently more than two million stock options that are already vested and another 936,000 RSUs (Zynga calls them ZSUs) already vested. He also has another 750,000 shares that will continue to vest due to his board position.

But, because he is no longer an employee, he is forfeiting all his unvested employee stock options and RSUs. Although it does seem like a lot, this is typical in such cases.

I need to go to lunch, so just read it for yourself:

ZYNGAINC-20111117-S1A-0

In a new filing with the Securities and Exchange Commission concerning its upcoming IPO, Zynga is expected to unveil two key management and board changes at the online gaming phenom:

Chief Business Officer Owen Van Natta — who came to the San Francisco-based start-up several years ago to help CEO Mark Pincus grow it and develop it — will step down from his job and become a strategic adviser focusing on major partnerships. He’ll still remain board member at Zynga, but will give up millions of pre-IPO shares by moving out of his operational role.

And director and venture investor Brad Feld will leave the the board, which VCs sometime do as companies move to a public offering and add members with more specific business experience.

In his place, longtime entrepreneur and investor Sunil Paul, who founded a company called FreeLoader with Pincus many moons ago, will join the board.

Zynga confirmed the changes to me in a statement by Pincus:

“Owen is a valuable business partner. He’s made great contributions to Zynga and continues to be an important part of our team.”

Sources said the changes related to Van Natta around are not part of a recent controversy around a Wall Street Journal story about clawing back of some share options grants of early Zynga employees who had become less involved in the company. While the company cannot actually take back already vested shares owned by those staffers, the article has put a lot of scrutiny on Zynga and raised questions about how to cope with the kind of hyper-growth some Internet firms experience.

That’s certainly been the kind of rocket ride Zynga has been on, as it has grown from a small social gaming company on Facebook to a high-profile public company.

Zynga is in the final stages of its IPO process, answering questions from the SEC that are typical. If all goes well, Zynga execs are expected to go on a road show after the Thanksgiving and go public by the end of the year at a market valuation of close to $20 billion.

That was different from when Van Natta officially got to Zynga in the spring of last year — after a rocky experience running the doomed Myspace. At the time, he told me at the time that planned to be focused on scaling the business and did not consider himself a long-term operating executive.

Since then, he has helped Pincus hire a series of experienced gaming execs, including a chief operating officer, a chief marketing officer and others.

Zynga was Van Natta’s third high-profile Web company in recent years. He was a top early exec for Mark Zuckerberg at Facebook until early 2008, and in 2009 he took over News Corp.’s (NWS) MySpace, a job that lasted less than a year.

Early in his career, Van Natta was also was a top strategy, marketing and deal exec for Amazon, which bought an early social networking start-up called PlanetAll that he worked at.

It will now be interesting to see what Van Natta does next, but it is unlikely he will take a permanent position. He is a longtime angel investor in Silicon Valley, including in hot start-ups such as Asana and still holds a significant stake in Facebook.

But, in moving out of his job at Zynga, he will be giving up many millions of shares of a rich trove he was given when he arrived at the company. That said, Van Natta already owns millions of accelerated vested shares and will get another large grant as a board member.

Translation: Don’t cry for Mr. Van Natta, Silicon Valley — he made $42 million last year from Zynga shares alone.

Quite the altruist, that Karmazin.

But let’s be honest here. Given that the options, of which 24,000,000 were vested and 6,000,000 unvested, had an exercise price of $4.72 per share and that Sirius’s stock is trading at about 35 cents, they really weren’t worth anything. So a nice addition to the company’s incentive plan, but an ironic one in that Karmazin had little incentive to keep the Sirius (SIRI) options he’s forfeiting.