Tony, I guess it depends on who you talk to as before I bought mine I did alot of ringing around chatting to specialists about the EJ25 engine. Some said its fine and don't worry, others said anything above standard bhp would need the engine doing beforehand as under "full chat" the gaskets would give in.
Mine has had alot of work done to it by the previous owner including having the engine out and new gaskets, seals fitted but the new parts were only standard Subaru parts and not uprated parts so I'm still abit weary about having a map although I'd love to have 330 - 340bhp.