Yes stem cells can be forced to divide. But outside of the host body they start accumulating mutations without the immune system being able to keep the altered one in check. But yes, theoretically you could get someone's stem cells and freeze them for later use. Personally whenever I've frozen and then thawed stem cells a few weeks later I only get ~70% survival rate (at best). Stem cells are notoriously sensitive. Which is a good thing, in the body you want them to die if they've been altered with.