I don't think it was hard at all, just hold a modifier key and paint over any other elements. Hopefully this makes it back soon, the feature is sorely missed!
You cannot cut signs. (they stay there instead of being deleted)
Just messing around, and I found a bug. Put down a chunk of ice and set its ctype to phot. Warm it up. It will quickly produce a pressure rise; most will disappear but some will fracture into snow which disappears in the next few frames. It causes a shockwave which rises to about 6.5 pressure in the center with cursor 14 clicks (of ]) above smallest. It's kinda cool actually, but still a bug.
This is not really a bug, when melting happens, it changes its type to PHOT. But because it was orignally ICE some values are not set to make every particle work. In effect these photons have no color, and there is code to specifically delete black photons before they appear. About the pressure I'm not sure what is creating it, state changing to an energy may be messing with something in there.
EDIT: Found the pressure, photons are for some reason considered a gas, transistions to a gas create pressure.
It would actually not be hard at all to give photons created from state changes a color, I'm not sure if this should actually be done, because photons would never be created from normal state changes in the first place.
Also, when you try to cut layered materials it only deletes the first layer.
TPT crashes when you try to fill an area with streamlines.