Hot melt is an over priced glue gun with a non hardening glue. It's main purpose, add swing weight to raw heads. Most OEM heads have a little black rubber plug, most likely hot melt was added for your D2, D3 etc swing weight. You can add it to the heel or toe for a bias but, most hot melt jobs are for swing weight. It can be used to dampen sound too. The big difference between lead hosel weights and hot melt is COG will be lower in the head. Most of the time Hot Melt is added through the weight portal, or the black rubber plug. You can use RTV to close the hole back up if you drill it out.
IMO...just add or subtract the OEM weights, lead tape etc. Hot melt is permanent, I'm sure you could add a solvent to the head and dissolve the glue but, not recommended.
Also, if I'm remembering my training, lead hosel weights move COG back toward the hosel. Please correct if someone knows differently
Enjoy your Hot Melting