Unfortunately, you can't change the rosters, in terms of altering ratings and importing players, so you are stuck with the players from the last official roster update in Jan. 05. What we do is have drafts, trades, and free agency. We know there is no chance to have realistic rosters anymore, so we just let every one be their own GMs, and have some fun with it.
The season we are currently in, we began with a "Vince McMahon" style draft to it. I pulled names out of a hat at home, in front of a couple of witnesses. I posted the names of the GMs on our league website. Next, each GM had to pick a team for SOME ONE ELSE (NOT their own) from a list of teams that I put together consisting of the least used teams in our league's history (teams like the 49ers, Cardinals, Bucs, and Titans, which were never used) and the teams that had underachieved throughout our league's history (Broncos and Colts, for example). The last guy who picked, obviously with only one team left from the list I announced, had the option to switch any 2 teams he wanted between 2 GMs, NOT including his own.
So basically, you had guys getting either screwed or hooked up. Or top "heel" of the league, who allegedly cheats occassionally, got assigned the 49ers with the first overall pick! Haha.
After that, we opened free agency up, with the free agency pool consisting of players from the Bears and Vikings.