I'd like to have an option to somehow disable/comment out lines in the search string.
Eg. I search for something like:

partyfit
and (tanks == 1 or heals == 1)
and (gd or yard or gmbt)

But when I want to see all dungeons I have to delete the last line. I'd like to do something like this to "disable" the line:

partyfit
and (tanks == 1 or heals == 1)
#and (gd or yard or gmbt)

Since you are actually writing a Lua expression evaluating to a boolean, you may simply use Lua comments:

partyfit
and (tanks == 1 or heals == 1)
--and (gd or yard or gmbt)

Or even inbetween:

tanks == 1 --[[ and heals == 1 ]] and dps == 3