I wanted to know if its possible to code the loadingscreen in Lua which players see upon joining my server, I’ve seen an file which sends the data and such, question is, if I would edit/overwrite it(per addon, duh) on the server, would it get applied on the players, so they see what I put there upon joining my server? Would be actually pretty cool if that would be possible.
Uh yes it is however the same functions are available. You’re at the mercy of the developer of the framework you use.
You can use Lua for the backend, but not for the front end, which is appears what OP is asking for.