First, you'll need GCFScape to extract the addons and edit them. You will also need the VPK files of the addons you want to merge. You can get these by either downloading from a website like Steam Workshop Downloader or finding them in your "workshop" folder under the "addons" folder in "left4dead2". To find the addons in the workshop folder, you will need to have launched the game with the addon installed at least once.

Now, you'll need to extract a VPK file's "root" folder to your desktop. If you are trying to merge conflicting addons, then extract the addon that you want to replace the files of with the other conflicting mods. Now, open the other VPK file with GCFScape and extract the contents of each folder within the addon to the "root" folder. You do not need to extract "addoninfo.txt" or "addonimage.jpg". If you are merging multiple addons, then repeat the process in the same "root" folder.

Now, your "root" folder is done. In the "bin" folder, you will find a application called "vpk.exe". This is located under Left 4 Dead 2>bin. It is NOT under the "left4dead2" folder with no spaces. Once you find this application, simply drag the root folder to vpk.exe. On your desktop, there should be a "root.vpk" file after you do this. If not, then simply go back to file explorer and click desktop on the left. Now, you will see your merged addon. If you want, you can rename it to anything you like.

After this, you are pretty much done. Navigate to the "addons" folder located under "left4dead2". Put the vpk in the "addons" folder and you're done. Launch the game and make sure it works. If it works, then you successfully merged your addons.

If you have any issues or questions, then ask in the comments.

Thank you for reading my guide!