Subaru's post 1999 can be remapped by ECU TEK software. They are usually remapped in real time on the road or on a rolling road.
Pre 1999 Subarus need a replacement ECU such as an Apexi, Motec or Autronic which then has to be set up by a remapping specialist who is familiar with that type of replacement ECU.
try loking up ECUTEK.COM
Frawls555