Add the "nomodifier" option to the first two lines so that holding down any modifier key will skip those two lines. This gives you the ability to change targets. Especially useful if you acquired a target out of range and the macro is now not doing anything.

Also, remove the "exists" keyword as the macro will automatically check for "exists" since you are specifying "harm".

/castsequence [harm,nodead,nomodifier] etc
/stopmacro [harm,nodead,nomodifier] etc