2012 Subaru Impreza hatch back

Its not so much hard with the right tools and knowledge as it is time consuming and expensive. Subarus are like legos, most stuff can be swapped around, but ECU, changes in wiring, different crossmembers, some cutting, etc. Nothing ever goes seamless or easy, but it's mostly just the cost and time to consider. You are talking about adding 50-80HP, which you can feel but is it worth the cost to get to work and back? Your call there, but possible, yes.