So, I'm just here to warn anyone who uses TF2Items_OnGiveNamedItem that replacing an item with one of the same class with a different item definition index may cause animation or attribute bugs.
I know for a fact that replacing the Amputator with the Bonesaw will cause issues where the Bonesaw is repeatedly pulled out for no apparent reason... and even with OVERRIDE_ATTRIBUTES set (and PRESERVE_ATTRIBUTES not set), it will keep the Amputator's higher healing rate. This is with TF2Items 1.6.0-hg258.
It appears that the way to correctly address this is to block the weapon and give them the appropriate replacement weapon when they respawn. This is what Prop Hunt Redux now does for all its weapon replacements in its latest beta version (beta 9).
__________________
Not currently working on SourceMod plugin development.