Problem with copying vertex weight

Hi, I’m having some issues copying vertex weight onto other vertex.

I have a body mesh, then I created an accessory (belly piercing) and want to rig it to the body. Is it possible to select 1 vertex on the body mesh, then copy that weight onto every vertex of the piercing? According to instructions from another user, I first joined the piercing onto the body mesh with ctrl+j, then select 1 vertex near the centre of the bellybutton, then selected 1 vertex on the piercing, and clicked “copy” under vertex weight panel. But this is not really feasible for objects with very high vertex count, there’s no way I can manually select thousands of vertices one by one and not expect to miss some.

I did some googling and found this script by Ivo Grigull: Unfortunately it only works with older versions of Blender, and those older versions of Blender don’t work with my body mesh.

So the question is are there other scripts or addons where I can copy/paste vertex weight more effectively?

Anyone know?