Of course you can weld it in Poser, but you lose all morphs if you created any.

1. Go to the Setup Room.
2. Select Figure_Name_SETUP (you can find it in prop list)
3. Open grouping tool window.
4. You can find there chest, collars etc groups - DO NOT CHANGE them, but press "new group"
5. Press "add all" and press "weld". Def welding 0.000010 should be ok.
6. Leave setup room and save your figure.