From multiverse to datapack dimension

Hi there 🙂
I'm tired of having my "execute in minecraft:.... run ... " as warnings in my server's datapack (VSC Interface), and i know why it happens : i've worked on many servers who were using Multiverse to carry dimensions, instead of datapacks, and i've now around ~14 different maps. My dimensions are then "unofficial" from the DP perspective.
So today i would like to reduce my need of multiverse by... "converting ?" the already existing maps into recognized datapack dimensions, but i've no idea how to just make my dimensions "official" and not create new ones, i'm not interested in real world gen for the moment cauz i essentially build all i need in flat or void maps. I saw there was a dimension subfolder in datapacks, but i'm afraid it just creates new dim and not register mines as DP-friendly... For the future i'll create them directly with DP.
Because my code already uses the namespace "minecraft:dimensionname", i suppose it would simply be files to add in the minecraft namespace of my main DP, right ?
If there's way to carry inventories differently too, i don't think i'll need multiverse anymore so that would be a good point. It would be awesome to end with only worldguard and build plugins to run the games !
What do i need to be aware off ?
Thx in advance for tips