Non-CAM dolls (Regular releases) lower legs do not come off. You have to cut them off, and then they are garbage:( The peg that keeps the lower and upper leg connected would be damaged, making the leg good for nothing.
You could wrap the the Regular doll arms in teflon tape to thicken up the peg. Use small amounts until you get the right thickness.
For more advice on the legs, I think I'd need more information on what you want to do
I could ramble on about what methods are out there for CAM mods, but I'd rather not do that:) Rambling = Yuck!