Hi Visconti,
To get something equivalent to "all /blabla":
In latest Textmate build, cmd-| ("|" is unix pipe character, not lowercase l or uppercase i) triggers "Filter through command". First select all text you want to search inside. Then press cmd-| You can then type "grep 'blabla'" as command. You can select how output will be handled.
I don't think there's a way to exclude/include lines interactively, but you can get pretty far by just editing the grep command, and rerunning it either on current result, or on the original text.
Allan, there seems to be a bug (or is it a feature?) where if command output is null, the selected text is not replaced.
Meryn