Re-importing an audio file to a multicam clip

This is a curly one.

I've made a video of me playing and singing guitar. Firstly I recorded the audio element in a recording studio, 5 singing with acoustic guitar tracks, then when we recorded the video component separately and I mimed to the audio track. Following that, I then synced them up with the 3 camera angles as a new multi cam file in Final Cut. Anyway, the agent who wants the video wants me to add more reverb to the guitar and singing parts and lower the vocal part of the mix. Only problem here is I've already completed the video.

So, my question. I plan to go away and add reverb to my vocal/guitar track and fix the audio up accordingly as the agent wants it. Does this mean I'm going to have to re-import the new audio track once its fixed and create a whole bunch of new multi cam clips? So effectively start the project over? Or, can I re-import the new 'fixed up' audio into my multi cam files that have already been created and effectively replace the old 'non reverb' audio to the video of me playing and singing these songs...... somehow?

I'm guessing its probably a no I can't, I thought I'd put it to the brains trust anyway.

Troy