Researching new applications of the Permanency spell?

[gadren]

I could've sworn I read guidelines in a WotC book about being able to research other applications for the Permanency spell (ie, other spells you can make permanent), similar to how you can research new spells.

I can't seem to find it anywhere now? Anyone know what I'm talking about?

[icefractal]

It sounds vaguely familiar but I don't remember where/if I read it specifically. Maybe Tome and Blood?

[Ravens_cry]

It's under the spell itself in the PHB at the very end of the Permanency spell description. It's subject to DM approval, and it costs the same as researching the spell you want made permanent itself would have, but that's where the rule is. Oddly, these rules are not in the SRD, which is why I am not quoting the exact text.*
*plus I'm lazy.