For some reason when ever I update the mod pack, and enable/disable certain mods when I go to hit "Launch" it re-downloads all the mods (Even when the mods are disabled) saying it's trying to download a texture pack... what gives?
I've been launching my custom packs with MultiMC 5. Getting it to work is a little... odd, but you can copy an instance over from the FTB Launcher.
1.) In MultiMC, click the little computer icon at the top (Change Settings)
2.) On the Features tab, under FTB, check "Track FTB Instances". That will create a FTB category with all of the modpacks you have downloaded. It does not create new folders for those modpacks, it just loads them straight from the FTB folder.
3.) Select an FTB instance, then click "Copy Selected Instance" at the top. Give it a different name and click OK. It might take a bit of time to copy. That will put the new instance in the default category. This new instance does not yet include vanilla Minecraft or the Forge install, that will be downloaded in later steps. It will copy everything else, just not Vanilla and Forge.
4.) Run the instance once to download vanilla Minecraft. If it gets stuck loading, you may have to use the "Kill Minecraft" button on the console the first time. If so, just run it again and it should work. The instance will load as Vanilla, so DO NOT open any saved worlds, just quit Minecraft and go back to MultiMC.
5.) Back on the MultiMC window, right-click the instance and choose "Edit Mods"
6.) Go to the "Version" tab and click "Install Forge". Choose "Forge 9.11.1.965", and click OK.
7.) Once it has download and installed Forge, click Close and go back to the main MultiMC window.
Now, when you open the MultiMC instance you will get an exact copy of however you had it set up in the FTB Launcher. I've done this with customized versions of Magic World 2, Tech World 2, and Direwolf20 1.6.4, and it's worked every time so far (though I have had to use the "Kill Minecraft" button on the first vanilla loadup for all of them). You can customize your instance either before or after transferring it to MultiMC, it doesn't matter. For my main pack, I just copied over Magic World 2 with the above steps, and then copy-pasted the extra mods I wanted (BC, TE, RC, a few others) from the FTB folder for Monster. You can disable mods from the Edit Mods menu in MultiMC as well.
Just be careful not to open any of your saved worlds until the main Minecraft window shows the MCP, FML, and Minecraft Forge version numbers in the bottom left, along with "# mods loaded, # mods active".