in your \UI\ProfitUI folder in the _ProfitUI_QuickRaidButtons.txt file
if you have a line like this for your class:
Code:
<Data Name="Button1" Macro="useabilityonplayer Parent.Target Regrowth" Tooltip="Regrowth"/>
you would insert
cancel_spellcast just after the
Macro=" bit, and also a carriage return between the two commands, like so:
Code:
<Data Name="Button1" Macro="cancel_spellcast
useabilityonplayer Parent.Target Regrowth" Tooltip="Regrowth"/>
As Eowaubeth pointed out, if you hit this button it'll cancel whatever you're casting, so if you start curing a DoT on someone, you won't be able to queue a heal on it's tail, as the heal would now interrupt the cure.