This suggestion is awesome. I always found the lizahrd temple was a little lacking in terms of loot. Besides the picksaw and sun stone if you want to make a celestial stone, none of the items are that helpful in progression, so adding some nice weapons seems pretty cool. The only problem I can see is that this makes all golem-tier melee weapons outdated, so the golem fist and possessed hatchet might as well be removed, or maybe nerfed and added into the pre-hardmode lizahrd temple with the toahd idea you had. (Pre-hardmode lizahrd temple anyone?) Maybe the temple key should last forever and be used to open hardmode lizahrd chests like how the shadow key can open shadow chests, and then pre-hardmode lizahrd chests would contain the nerfed hatchet and fist.