Macro, skip cooldown?
 

Is there a way (maybe a mod if not in macro) to set a spell to cast, and if it is on cooldown, cast another spell?

I'm no expert, but I think what you want is impossible atleast in a macro.
It would allow for automation of gameplay, which is against Blizzards rules.

Dunno about addons.

AddOns and macros are subject to the same stipulations; what you want is strictly not possible.

ok cool.. thanks!