I cant say anything about the fact one might have a fiberglass handle, but I wont try to forge any of them unless it is made in the US. The name brand hammer makers generally used a steel that is shock resistant and would work well for a forging hammer. I look for Vaughn, True Temper, Stanley, Plumb, etc.
If you reshape one, be prepared to make any corrections to the hole by having a drift handy. Lin