I tried it myself and it didn't budge.

My fiber print was dry mounted to an archival backer board using low temperature mounting tissue. I reheated it to higher temp than used to see if it would loosen. It didn't.

It might be a case where you can cause more damage than just leaving it alone.... I was just testing with a junk print so no loss for me. If it was a one off deal like yours, I wouldn't try it....