spell/line negation

I would like to see a character that can be used to negate a line or a spell. Such a character, perhaps pound “#” when put in front of a “/cast” i.e #/cast spell" would negate that line in GSE.

And also, the same character to be used to negate a spell in a castsequance i.e /castesequence spell1, spell2, #spell3, GSE would just skip over spell3.

The use for this as an example:
Halo is a priest talent that heals and does damage, with a large radius, on some boss fights, there are mobs that are CC’d and at that point if Halo is used, it will break CC. With the above ability, that spell or cast could be negated very quickly between boss fights without having to delete lines and than remembering to put them back and where in your GSE macro, etc…