The stype property would work much like the ctype one, but will specify the source type the element is operating on, e.g CONV (GLOW) [WATR] would convert only WATR to GLOW.
Maybe middle click?
Aww, forgot :P
Maybe a STPE tool? It would use the last used element as the type.
jacob2, maybe FILT to match and replace stype to ctype in BRAY/PHOT. Example: BRAY(12345) + FILT(1337)[12345] = BRAY(1337). Also, it could be used to make STKM immune to a specific element, etc.