Is there any CLUA command that creates/inscribes a spell directly into your spellbook? Because I want to be able to use custom spells with my sorceror.

This worked in Icewind Dale, but I haven't tried it in BG2 yet. The code was AddSpell, and would (in BG2) look like this--

CLUAConsole:AddSpell("spwixxxx",n);

where xxxx is the spell code (check Infinity Explorer) and n is how many times you want the spell to be memorized. AddSpell("mage"); would add ALL mage spells into memory!
Alternatively, you should get Shadowkeeper to edit your memorized spells.