lol, happens to everyone, in fact me and my buddies usually take a bet when we get a jdm motor whether or not a stud will come out of the head when i pull the exhaust manifold. haha ive had very very few motors that i had none come out, Usually get at least 1 that will pull out, i just put it back in and tighten it down good and have had no problems ever with any exhaust leaks, Use the newer style metal exhaust gasket as well and you wont have any problems guaranteed.
Again even with the ones that pulled out just put them back in the same spot and ive never had one back out on me or come loose.