Need to break glue joint
This will be a little long so that you will know "where I'm coming from". Man who is brother of (deceased) wife of my late uncle was getting ready to go to nursing home, cleaning out his house. Gave me a table and told me it once belonged to my Grandmother. Top about 22" square, quarter sawn oak glued up from 3 pieces. 4 round turned legs with claw and ball lower ends. Table a bit over 36" high. Middle shelf of 2 pieces of QS oak with glue joint in center of shelf width. Shelf and legs held by pocket screws from the bottom of the shelf in each corner. Obviously refinished (by him) and beautiful except for one problem. The shelf joint is a modified tongue and groove and must have been reglued as some squeeze-out shows through the finish. The edges of the two pieces slipped laterally about 1/4" while in the clamp- uneven at the edges at the joint. Obviously I cannot saw it as the kerf would reduce the width of the shelf. I need to cause the glue joint to fail. It is almost certain that he used just a white glue. I know that those fail under continuous large loads, heat, and humidity. I do not wish to damage the wood. Perhaps he failed to remove the old hide glue completely before regluing- which might be a help in breaking this joint. But pressure to break it will have to be applied so that the pieces will slip laterally against each other. Any other forces might break the tongue. How much heat/humidity can be applied without damaging the appearance of the wood? The finish can be redone if necessary. Your suggestions?