As someone with at least a passing interest in Uniform numbers (see Cubs By The Numbers by Al Yellon, Kasey Ignarski and Matthew Silverman) I found this little note in the story on the new labor agreement.
Quick uniform number switches will be a thing of the past. Players must tell the commissioner's office by July 31 of the preceding year if they want a new jersey. That is, unless "the player (or someone on his behalf) purchases the existing finished goods inventory of apparel containing the player's jersey number." As in, every replica jersey, jacket, T-shirt, mug and anything else with a number that's anywhere in stock.
I guess this would put an end to the deals that a new player to a team would make with an existing player to get his old uni number back (unless the new player wants to pay for all the old existing stock of the old players merchandise). I would think it would also make the 3 uni number in a year people (see Ryan Theriot in 2006 & Roberto Pena in 1965) a definite thing of the past.