Creating An Additional Learnable Menu of Spells?

Could Catone's code be linked to inventory items the way tools is?

No. Catone code use partially Magitek's code, at the point of modifying the patch to make it behave like Tools you better start from scratch and use portions of Tools code if possible. Tools is more complicated, you have to reserve some RAM for the owned tools (or look items each time Edgar use the command). If you want to use spells like Flash and without special effects like some other Tools, you'll need to expand the $C2 Skean / Tools spell IDs table. If you want special effect you'll need another table similar to the Tool table in bank $C2. I'm not really familiar with the battle menu code, how to hook a new skill to existing menu or do one from scratch so I'll stop here.