at the end of the day, its mod at ur own risk. nobody can preciesly tell u what the warranty ramifications are with exhaust and particularly, ecutek. it'd be a smarted move to buy a full replacement (not flash or piggy) ecu and on the slim chance you have engine warranty issues, u can put the OEM ECU back in. it's not like subaru dont know about ecutek, so im sure theyve got some means to check to see if its been reflashed.

but if i were u and u'r worried about warranty, just do the zorst and intake. ride the warranty period out. and then start modding to ur hearts content.