Hello, I'm trying to make a mod that will allow users to play with their own resource pack on a server that sends you a resource pack and will kick you if you don't let it download (i.e. have resource packs set to enabled). I only know basic modding and have created mods through looking at other mods and following their example, but I can't find a mod that loads resource packs, detects when it is being sent a resource pack from the server, and is able to 'trick' the server into thinking the client is using its resource pack. If you can offer any guidance it would be much appreciated, thank you in advance.

Pointless idea, there is a reason server requires resource pack.

 

Anyway - it is possible (everything is), but just note that it is not only not-basic but also requires quite some Java knowledge (probably Reflection).

This mod can be clientSideOnly (look at @Mod).

All resource packs are being held in Minecraft#defaultResourcePacks (or name of sorts). After being downloaded and loaded by client, they will (probably) be there. You will need to simply force replacement. If you want to do it "smarter" and cancel downloading all the way, you can probably hook into packet pipeline and catch packets that in any way ask about resources.

 

I wouldn't really expect anyone here to tell you exacly what to do, this is totally not standard idea and if it hasn't been written alredy, there is a reason for that.