Interchangeable Parts

You can slightly round out an existimg peg so that it pops in and out easier. To that the parts all have to be modded so that the pegs are all the same. Round the first one and keep stopping to check if it pops in. It should still need a little force to go in so the joint isn't too loose. Once that one is satisfactory, do the others the same way keeping the working one close by as a guide for the shape.
Another way is to wrap the peg in teflon tape (used for plumbing) and put sculpt in a limbs joint hole and smooth the sculpt around in the joint hole. The teflon tape will not stick to anything including sculpt. Now a smaller peg fits the larger hole. If you have trouble removing the limb try blowdryer as some peole have had trouble boiling sculpt.
Or get screws all the same size amd drill a hole in the peg to fit the screw careful not to make it too large. Use superglue to cover the screw and screw it in the hole you drilled. Use the bur dremel bit if the peg hole is too small. This is similar to fixing a broken peg.
Lastly, neodymium magnets, like the ones used in gaming mimiatures. Glue a magnet to the peg and if needed drill the peg hole down to accomodate the height of the magnets then glue one in the peg hole. Let them dry before attaching together. Be sure to mark the poles so they don't get mixed up with a permanent marker and that all pegs poles match and all holes poles match. You cam alsobise round steel balls such as in a shoulder joint or head joint to replace it. Sculpt around the balls and be sure the balls and magnets were glued first.
GOOD LUCK BRO!

A lot of people like to use magnets, but a simple peg/hole interface is also a dependable method.