I have never replaced a rod without removing the head but have heard of it being done. From what I have heard you can get the piston down low enough to slide the wrist pin out enough to change the rod. I would really take a close look at things and see what else needs attention. Especially if it had a rod bolt laying in the pan and it had been run that way. I would check the clearance for the rest of the bearings at a minimum. The end results of patching a patch job usually end up with a bigger mess.
Good Luck Don
