Like I said, my knowledge is limited in Subaru and I've forgotten more than that in VW! I figured the exhaust cam would be less aggressive in FI applications versus NA.
If you have piles of spare cams, a head and some cam gears, by all means experiment away! Its what I did when I delved into the dual exhaust cam mod for VWs. Before all of this though, make sure the bearing locations etc are the same and that the cam will fit in it repurposed location.
When I did the mod, the cams were solid cast steel so I was able to cut and score them with a cutting disc on an angle grinder, smack the scored end off with a hammer and then finish off the end on a grinder. Like I said, I don't know how Subarus are but I'd imagine the construction is similar.
I would recommend at least eyeballing the cams first with the correct gear for the side (intake cam gear on the exhaust) just to see if you can get the center lines and lobes close or even if the lobes match. You can probably tell by just looking at both from the cam gear end and comparing the location of the cam gear pin to the closest lobe.
Once you've done that, you can determine if you can dial out any advanced or retard with a cam sprocket, which you'll want anyway for fine tuning.