for the Xbox 360 and PS3 Versions do the following steps
After loading up the game under the main menu go Rosters and Go to the Roster Magament Section press the button that you use to change teams then scroll till you see HOF Unlocked pool
all the HOFamers are in this pool after getting to the HOF pool On the PS3 Version click the X button a box should pop up asking if you would like to release that hall of famer to the free agant pool
note: you can only release hall of famers 1 by 1 not all at once so pick the hall of famers you want and release them to free agents
then go to the free agent pool and assign them to a team or start a franchise with them in free agents but make sure u have the hof on before starting a chise and you should be set hope this helps thanks
P.S,. i also found out these exact same steps can be done during a fanchise as i just tested it i was able to release the hall of famers to the free agents pool in franchise so either way can be done thanks