as the same way you incress w/e ability via triggers...
As example:
Trigger:
- Unit - Set level of Starfall(inspelbook) to 2 for Triggering unit
will incress level of starfall in a spellbook to 2
Trigger:
- Unit - Set level of Starfall(notspelbook) to 2 for Triggering unit
will incress level of starfall outside a spellbook to 2
as the same way you incress w/e ability via triggers...