10-speed chain too short, can I add links?
10 speed chains aren't designed to rejoined like 7 speed chains. The outer plates are thinner and the pins sit flush with the plates, which leaves little margin for error when reinserting the pin. The pins are often riveted too so they can't be correctly reinserted even if you are able to perfectly line it up. I'd use extra connector links instead of trying to reinsert the pin.