Nevermind, I actually made it work by selecting "Diplomacy 4.1" instead of 4.3 on Tweakmb

Ok, first off, i'm a novice modder at best, so take everything i say with a pinch of salt. Rocki is correct, when you search for the workshop file you need to use Diplomacy 4.1 However. There is a process to make this a little easier for future modding. Firstly go to //Discdrive\\:\Program Files (X##)\Steam\steamapps\workshop\content1 Then search for the number: 48700, inside that folder is another folder numbered: 285119009. Copy this file. Then go to //Discdrive\\:\Program Files (X##)\Steam\steamapps\common\MountBlade Warband\Modules. Paste the folder we copied into the modules folder. Then rename it to "Diplomacy 41 modded" (we use 41 instead of 4.1 because some folders won't let you use decimal points) This diplomacy file is the one we will be using. So next we want to boot up tweakmb. Then select "Load module warband". Then search the list for Diplomacy 4.1. It will ask you for the file location, this is where we go to the file we renamed to diplomacy 41 modded. We select this file. Then we mod away. Enjoy. *ADDITIONAL* For moving your save files between each version, boot up the new launcher (diplomacy 41 modded) and play the intro and create a single save. This creates the folder we will need. Then exit the game, go to your documents, and find mount and blade warband saves folder, then move the save from "diplomacy (steam workshop)" To diplomacy 41 Modded.