For a campaign I'll be running based loosely off the Ruins of Azlant AP by Paizo, one of the magic skills I'm going to allow are a variant of the Runes magic skill in Terrinoth.

Instead of carrying little shards with a mystic rune engraved on it, the runes are carved directly into the skin. It uses Brawn instead of Intellect, and the default range for the Attack action is Engaged instead of Short.

This will be my first time running/playing with the magic rules, though I've listened to episode19 of DPP. Do these changes seem unbalancing?

Will All players be magic users of, some kind or is it just an option?

Brawn as a stat does alot of things like soak, Damage encumbrance and wounds. So it might be 2 good an option especially in a fantasy setting where alot of combat is meele

But it will not break the system it might create some ubalance in some situations if you have other non magic users melee characters the Rune tank will likely outshine them.

Would having the skill use Resilience in place of a Knowledge to alter the effects of a spell work better?

Must combine with this.