I work on a homebrew of a wizard that will be able to select spells from all other spell lists but casting spell from spell lists not of the wizard will cost a spell slot higher by 1.

So 9th lvl spells are not an option and cantrips of other classes will cost 1st lvl slot.

• I want to change the cost of spells in term of spell slots, is it possible?

The idea is that access to spells of half casters will be granted through features because otherwise the wizard will be able to cast them very quickly and that will be OP. Is it possible to do that?

Thanks

Not currently possible without homebrewing altered versions of each and every non-Wiz spell to be a level higher than normal.

Ohh boy, I mean I do homebrew but that's a bit much.

Thanks for the reply.

What about granting access to the spell lists? I want to allow the character to add the spells at least the their lists.

I know it's not really getting into the technicalities of how to accomplish this on D&D Beyond, since that seems to be more your concern... but design-wise, I wonder if it would be easier to balance if the Wizard has a limited number of spells they can acquire from other spell lists. Like... instead of giving this class the option to learn spells from any class permanently as wizard spells, they could have a feature where they can prepare a limited number of spells per day from other spell lists. Like... just getting the option to prepare a single spell per day from any spell list opens up a LOT of options.