Mornin'!

I'm not sure what you mean by a 'purchasing a modified' one.
There are several firms that can 'flash' your existing ECU; essentially you just pull your present one out, ship it to the firm, they reprogram it & ship it back to you, overnight usually. Then you just re-install it & voila', you're good to go!
Many members have their ECU's reprogrammed, indeed when I can score enough bucks that'll be my next mod. Do a search on "ECU" & you'll discover lotsa threads about the subject.
Good luck!