here is the best chart for comparing -
http://buy.red-mods.com/Comparison.htm#NBA2K12PCYou should be OK with the 'developer' license, and the modding interface allows you to have more than one roster open at once. MyFriend adds a panel that explains all the values, but there is a tutorial pdf included with the REDitor, so yea.
IMO, your process should be similar to this;
Get base roster (whether you make 1991 or use 1993)
Make sure all trades and retirements are completed from that year
Add "rookies" from UBR Draft Class files over retired players and/or legend/dev players (they start around ID 418 iirc)
Update Art (logos, jerseys, floors) for the teams if they have a team in the UBR or other year's roster (arenas tab, uniforms tab, teams tab)
Update the teams tab to make sure all the needed players are in the main rotation (this controls what player is on what team)
and then so on each year,
I will be honest with you, its a lot of spreadsheets and the roster can be a pain in the ass, this will take a lot of work. It might be easier to load the 1993 roster in association mode, controlling all 30 teams to prevent CPU trades and FA signings, load the 1994 draft class, go through the draft like what really happened, then use the Roster Exporter in the REDitor to export the association roster to an actual roster. Then continue the process with additional draft classes.