A few things I can think of:
Move the 'veterancy_action' from sbps to ebps and use a 'change_target_action' with 'change_target_type' is 'squad'. The ebps action will not be runned again upon recrewing.
Or put the 'veterancy_action' in a requirement_action and add an upgrade to the entity (set 'apply_to_entities_in_squad' to 'true'). Then check in the requirement to not have that entity_upgrade so it will only run once.
Disabling disembark is also do-able.
Clone abilities\aef\timed_ability\vehicle_decrew_generic_mp and add the requirement 'not' and in there 'required_unit_type' with 'unit_type' is 'tiger_ace'. There are 3 other decrew abilities, you have to edit them all:
abilities\aef\timed_ability\vehicle_decrew_m20_crew_mp
abilities\aef\timed_ability\vehicle_decrew_medics_mp
abilities\aef\timed_ability\vehicle_decrew_vehicle_crew_mp
Thank you for the response. I ended up puzzling it out myself out of impatience, cloning the blueprint for the tiger ace crew and adding "_recrew" to the end. For that squad blueprint I removed the veterancy action.
Then I just went to the recrew tab on the tiger ace and switched the crew blueprint from the normal squad to the recrew squad. So now any recrewing squad doesn't get vet and it worked out alright in the end.
Also thank you for the explanation of how to disable disembark on tanks. I was confused and thought it had something to do with whether or not the tank had an entry for the AEF race.