I'm not sure the plug could be inserted from the inside, so someone would have to test the possibility. I'll be rigging/loading my boat on Sat for an upcoming CBBT trip. If I remember, I'll try.
Remember the plug is tapered, so you couldn't replace it with a threaded bar with square ends on both ends (for inserting/removing from either end).
I have a rubber expandable plug hanging on a string in the bilge, so if I ever forgot to install the brass plug before launching (remember I store on a trailer), I could in an emergency plug the hole from the bilge side of the transom.
Bottom line is that as long as you either put OMC Triple Guard grease or teflon tape on the threads before inserting the plug before placing the boat in a slip for the season, you shouldn't have trouble removing in when pulling the boat in the fall.