I added ethanol to my TRizol RNA extraction
My answer is based on my experience in the lab and something like a best guess - it may or may not work. But given the fact that added 100µl of ethanol to 500µl of total volume and since water and ethanol mix completely, I would give it a shot.

I don't think that the ethanol would change the polarity of the solution so much that phase separation is inhibited. The only thing that I can image is the contamination of the aqueous phase with traces of phenol, so I would probably clean up more carefully and do an additional NaOAC/ethanol precipitation at the end of the procedure. If you expect a small pellet with little nucleic acids, add some glycogen to get a better outcome there. I would appreciate it, if you could comment on your experience (and the outcome) when you try to save you sample.