Lol it's not as easy as you think, it's not super hard either but yeah. just check some files like this:
https://github.com/ElunaLuaEngine/ElunaTrinityWotlk/blob/a57c51bf9cf0a11ee297da48fb1c0405d7efcf0d/src/server/game/Handlers/ArenaTeamHandler.cpp
https://github.com/ElunaLuaEngine/ElunaTrinityWotlk/blob/a57c51bf9cf0a11ee297da48fb1c0405d7efcf0d/src/server/game/Battlegrounds/ArenaTeamMgr.cpp
They are quiet easy to understand, but try rewriting everything from scratch, and 5.4.8 core is A LOT different than Trinity. So hopefully you understand that developer job isn't that easy, plus only thing that you get from it is people crying about changes and fixes.