you can use the catback utility within catia under tools>utilities>downwardcompatibility but it is highly suggested that you only do this on basic parts. any advanced surfaces may change as with any translation. basically the math between versions is getting more efficient when you go...
Antoine,
you can either not load the smarteam integration to catia on the machine or just give the user the access to do both at his descression. as for a login script i dont know that it is very logical, why would you like to do this?