Did you figure this out? I used an audio tape portastudio decades ago and it had a simple switch for adding reverb after recording so in the mixes I have from those times the added reverb at key points sounds really cool. Not sure how to accomplish this with the BR-800 though. I've just had to set the reverb up front for whole songs.
Punch-in/out when recording is one way. Might be easier to copy the (vocal) track in question to a new track, add the FX, then during bounce/mixdown, use the faders to go from the non-FX track to the FX-track (and back).