Hello there,

This might be a stupid question but I cannot figure it out. So my problem is that I don't know wich 'code', or better 'id', I have to type in for replacing Quartz Slabs with Stone Slabs. They both have the same id (stone_slab). I've looked online but found nothing. Is this possible, and if so which 'id' should I use?

Sincere,
Xalopune

Whoops just figured it out :)

I had to use the variant property so it looked like this:
/schematicaReplace stone_slab[variant=quartz] stone_slab[variant=stone]

So this will replace all the Quartz Slabs with Stone Slabs

Yep, you use block states for this.

Worth noting that (at least if I recall correctly) doing stone_slab[variant=quartz] will target both upper and lower slabs and they should maintain their side after the change.

Yes, it does target both and keeps the respective state value (upper/lower).