they wont know the difference between the two, but there will be a fitment issue there, so they might throw a red flag. as long as its the stock downpipe with 2 cats on it u might be able to get away with it.
not sure how well it fits on a legacy tho. because the 05-09 lgt downpipe is different than 02-07 wrx downpipe.
i would recommend getting a stock lgt downpipe if possible.