Probably simplest to apply penalties for using or doing stuff with equipment outside a character's tech level (see Equipment Issues in the Adventuring chapter). For learning the needful to understand a lower tech level, perhaps 5DP Talent, for going up a tech level, perhaps 10DPs. Depends on how much of the lower or higher tech level the character really wants to acculturate themselves to. If it is just one or two items of kit, then this is overkill.
Best wishes,
Nicholas