Probably a stupid question but I want to edit the Atlas of Endless Horizons so it can be given to a cleric in my party. I can see where to change the "Attunement by..." part of the item but how do I change it so the spells become cleric spells while attuned? The item as is has "these spells count as wizard spells while attuned" in it's text but I can't see what's been done so that the couple of spells that aren't wizard spells become wizard spells

Nothing has been done to them. That bit of text is all that is required.

So if I just change it to read "these count as cleric spells" my player will be able to access those spells even if they're not normally cleric spells? That's unexpectedly easy

They should be able to use it even if you don’t change that wording. It’s just plain text.

Cheers, I’ll give it a go

Happy to Help. If it doesn’t work lemme know.