So ... its actually not impossible, but it is a little bit of a PITA. Here is how you do it.
First, install the version of Forge that you want to use into your vanilla launcher and make sure it works using the vanilla launcher. I installed Forge 10.13.0.1208 to test these instructions.
There are two parts updating the modpack to use a new forge: Updating the modpack's JSON file and adding the library files.
First step is that we need the new library information for the version of forge you have installed. Find your minecraft/versions directory. On my Mac, it was in
~/Library/Application Support/minecraft/versions but on a windows PC it will be somewhere else. Once you find this directory, look for the new forge version that has been created. On my system, it was
1.7.10-Forge10.13.0.1208 . Inside this folder, you will find a file that ends with
.json. Open it in your favorite text editor and look for a section like this:
Code:
{
"name": "net.minecraftforge:forge:1.7.10-10.13.0.1208",
"url": "http://files.minecraftforge.net/maven/"
},
Copy that section into your copy buffer and move on to the step of updating the modpack JSON file.
To update the JSON file, find where you have FTB installed. On my mac, I have it in
~/Minecraft/FTB but you probably have it somewhere else. Look for a directory called
ftb_17testpack and that is your "Unstable" modpack directory.
In that directory, look for a file called
pack.json and open it in your favorite text editor. Look for this section:
Code:
{
"name": "net.minecraftforge:forge:1.7.10-10.13.0.1199:universal",
"url": "http://ftb.cursecdn.com/FTB2/maven/",
"checksums" : [ "346775fce838d4a139362d3b0135fd2aebba288d"]
},
Replace that section with the code you copied from the minecraft folder:
Code:
{
"name": "net.minecraftforge:forge:1.7.10-10.13.0.1208",
"url": "http://files.minecraftforge.net/maven/"
},
Don't worry if it doesn't match exactly as you may be using a different version of forge. Save this file and move on to the next step.
Next, you need to copy over the necessary library files. Find your minecraft libraries folder. On my Mac, it was in
~/Library/Application Support/minecraft/libraries. Once in the libraries folder, navigate to
net/minecraftforge/forge. In this directory, you will find all of the copies of forge you have installed. Keep this window open because you will need it in the next step.
Find the FTB libraries folder. On my Mac, this was in
~/Minecraft/FTB/libraries. Navigate to net/minecraftforge/forge. Copy any folders that are in the other window you left open in the step above (on my Mac,
~/Library/Application Support/minecraft/libraries/net/minecraft/forge) to the folder in FTB. The goal is to make the folders look the same. If files already exist, there is no need to overwrite them.
Once you have modified the JSON file and copied over the libraries properly, you should be up and running with the latest forge!
Proof of life:
Code:
[02:13:28] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[02:13:28] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[02:13:28] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker
[02:13:28] [main/INFO] [FML]: Forge Mod Loader version 7.10.25.1208 for Minecraft 1.7.10 loading
[02:13:28] [main/INFO] [FML]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.7.0_55, running on Mac OS X:x86_64:10.9.4, installed at /Library/Java/JavaVirtualMachines/jdk1.7.0_55.jdk/Contents/Home/jre
