@NJCJOE I was going to suggest using 1 inch pink foam insulation and carve out the joint lines. Does not look like you have room. Alternative is foam core and either apply the printed stone or scribe joint lines into the foam core. I painted a wash of sanded grout onto my carved foam for the textured look. I would think you could make these removable so you need not worry when you do other finishing. You could get additional texture to the walls by having the columns hiding the seams stand proud a little bit. If you really want to get crazy, cut out individual blocks from heavy craft paper and glue those to the walls leaving a gap between.
In the photo below, the portal on the left is a commercial urethane foam casting (deep relief cuts, company is out of business), The walls on the right are pink insulation foam scribed or cut then painted. Depending on how deep a relief you want, firm pressure from a ball point pen may work. For texture on the foam, a crumpled ball of foil pushed into the wall works. There are rollers made to make indentations into clay to simulate brick and stone work. Supposedly those can imprint into foam as well. Or make them out of clay and let air harden or get the oven harden stuff.
This is just an example of layering cardstock. Colors are from pastel chalks.