Like an XYShrinkWrap? I had a script for that which worked in 2012, but not for 2015 unfortunately. Give it a look around the web if you can find one that's up to date.
If you triggered it via keyboard shortcut by accident or through a script, it might not have updated the icon in the main menu. Hit "A" on your keyboard and see if it goes away.
Yeah, it's not the most effective method and does take longer. I know there was a thread about baking by material id's and some exploded mesh script renderhjs was working on.
there is a script for max4 and up, on scriptspot http://www.scriptspot.com/download.asp?ID=1069 that allows mass changes to keys, but I would think there might be something better in max7
the weld works, but only within it's threshold distance. I'm not sure where to change that in the default unwrap window though, but it is in the sidebar list with the chugnuts uv tools script.
Turn off isoline display. I wrote a little script that replaces export/export selected. It just turns off isoline and then exports. simple but a life saver.
Why do you need to do that? It should be possible to make a script to save the lightmap(s) after baking and then reassign them after baking the other set.