What you do, is declare the variable twice, each one with a different tag.

Variables

Name Tag Value
groundmount priest Swift Green Hawkstrider
groundmount pally Summon Charger

You make sure you tag your priest with the priest tag and your pally with the pally tag.

Your macro

/use #groundmount#

will have groundmount substituted correctly according to the tag that each character has.

Does that make sense?

P.S. Make sure you are using the latest build (12 I think).