need help trying to figure this out

hey guys ok so I have this macro for destroy

/castsequence reset=target Curse of the Elements,null
/castsequence reset=target Immolate,Incinerate,Incinerate,Incinerate,Incinerate,Incinerate,Incinerate, Incinerate,
/castsequence reset=0.8 0,Conflagrate
/cast [combat] Dark Soul: Instability
/targetenemy [noharm][dead

and it works great but ther are some fight where I have to use f&b a lot is there a way to add f&b to this and have it on a mod key so that when I push mod key it cast it and then when I hit the mod key again it turns it off

Add a line the top
/cast [mod]spellnamehere;

It will fire off that spell when pressing the macro and a mod button, alt shift or ctrl.