Installing it probably wont be that difficult.
Of course, that is coming from somebody that has pulled barrels out of replica's about 50 times or so.
Easy steps to take:
First find out how to disassemble the replica (maybe in manual... if not search the internet), then find out how to take the receiver off of the barrel, the barrel should be in view and you should be able to pull it out (may have to unscrew a few things first).
Since you will be putting everything back together anyways, I would recommend switching to a new hop up rubber to increase performance. I prefer Systema hop up buckings, but it differs between players.
When putting the hop up unit on the barrel, first put a little silicone oil on the hop up bucking so it slides in easier. Also, make sure you adjust the hop up unit so it looks as though it is doing its job correctly before putting the barrel in the replica. Other than that, putting it back together is like taking it apart but in reverse.
If you have questions, let me know...