For the war effort, I’ve gone through my old script library and picked out some of the choicest bits I wrote back when I was still trying to be a tools programmer. WeldTexVert is a modal window that’s automatically added to your UnwrapUVW menu bar that lets you interactively weld texture vertices in the same way you would with editable polygons.
The good news is that you can bind it to a hotkey so you never have to worry about the original weld vertex tool ever again. The bad news is, you need to select the UVW vertices you want to weld before opening the window. Sorry about that!
Either way, I hope you enjoy the tool.