A Few questions on modding

[regret]

Hi guys,

I am sort of interested in modding some stuff. I figured I will start with modding individual nations(units and equipment) first than later spells.

My main goal will be to eventually create Forgotten realms nations and also DnD type spells and magic items.

I have started some work on the nations and so far its been ok.

My main questions are

a: would it be possible to completely replace the magic items with self-created items or can i only mod them?

b: can i totally replace the spells ingame with my own spells?

c: can i change the name of the spell schools? Plan is to use traditional DnD spell schools. this is more for flavor and also to make it easier for me to organise where the spells are supposed to go.

Thanks for any answers in advance.