How you guys can generate older worlds in 1.17

I really love how the new minecraft caves look like and in order for them to fit in the overworld was increasing the height limit and making bedrock level lower, but this is what prevents older worlds to generate in 21w06a and up, so here's how you guys could be able to upgrade old worlds to 1.17, you guys can make the deepslate level generate in pre-existing chunks replacing the bedrock at y=0 and the air blocks from y=-1 to y=-56, with the bedrock generating at the last 4 levels.