[soltakss]

It depends what you want to achieve.

Do you want Wealding Magic to change to conform to a particular spell system or do you want the spell system to mimic Wealding Magic?

What I would do is to decide how you would like Weadling Magic to appear in the green, what effects you want it to have and who would be able to cast it.

Then decide on what spell system best allows you to do this.

If you want people of the Cat totem to be able to cast cat-like spells but not to be able to cast other magic then link spells to totems and give a cast chance based on the totem, so people with the Cat Totem have a skill Perform Cat Totem Magic and can cast cat totem spells but can't cast Rat Totem spells.

If you want someone to be able to cast some spells from the Cat totem. some from the Rat totem then give each spell a cast chance and let people learn spells individually.

If you want some people to be able to cast spells of a certain type, for instance Fire-based magic from the Volcano-dwellers, then give them special rules for casting their own spells.

I wouldn't make it too complicated, though, and I'd make the spells pretty much equally as powerful or use the same sort of mechanics otherwise you'll have over-complex rules for a simple setting. But, perhaps that is what you want - a setting where different cultures have vastly different spells.

What I wouldn't do is to use the BRP spells straight from the book. From what I have seen the BRP system has a very limited and not particularly defined magic system. That's fine for what it is as different settings would require different magic systems and a generic rules system shouldn't have all the different types of magic - that's what supplements are for.

But, I wouldn't be afraid of defining my own magic system for the Green, if that's what you want to do.