I don't know about vJASS, but this is easy to implement in GUI:
1, create 2 spell
- an empty_spell allow you cast on target
- a real spell that give X hp regeneration
2, write trigger :
- when empty_spell is casted on target:
--- healing x hp based on its primary attribute ( need write some code to do calculation)
--- add regeneration to target unit
--- if your regeneration spell do not have duration, try work out how to remove this regeneration after Y- seconds