OK, then lets go step by step:
I assume you have Modtek & BTML and have directly edited the SimGameConstants.json in ...\BATTLETECH\BattleTech_Data\StreamingAssets\data\simGameConstants
If so replace the SimGameConstants.json with the original, but keep your edited file, you'll need it later.
Now we start to make your own mod (will call it "MySettings" for the example):
1. Go into the "Mods" folder inside the "BATTLETECH" folder. There you create a new folder for your mod (...\BATTLETECH\Mods\MySettings).
2. Since you just want to change an existing file inside the "StreamingAssets" you have to recreate the folder structure from StreamingAssets" to the file inside of it, in this case: "StreamingAssets\data\simGameConstants" so that the complete path is ...\BATTLETECH\Mods\MySettings\StreamingAssets\data\simGameConstants
3. Copy your modified SimGameConstants.json into ...\BATTLETECH\Mods\MySettings\StreamingAssets\data\simGameConstants
4a. Now you have to create a mod.json for your mod, since you won't have a tool to create one, simply copy the mod.json from any of the mods you are using into the folder of your mod (...\BATTLETECH\Mods\MySettings).
4b. Now you edit the mod.json in your mod folder that is has the following content (starting with { and ending with } ):
{
"Name": "MySettings",
"Enabled": true,
"DependsOn": ["JK_VariantsCampaign", "NameOfTheVulcanMod", "NameOfTheJavelinMod" ]
}
Replace NameOfTheVulcanMod and NameOfTheJavelinMod with the real name of the mods, which is the name of their folder and also noted in their mod.json's, but keep the ""
Done
A little bit about how it works:
When Modtek finds the StreamingAssets\... folder structure inside a mod folder it merges all files inside with the game files at game start (provided that the file name and path, starting at StreamingAssets, are the same)
"DependsOn": ["JK_VariantsCampaign", "NameOfTheVulcanMod", "NameOfTheJavelinMod" ] tells Modtek that it has to load the mods with the names JK_VariantsCampaign, NameOfTheVulcanMod and NameOfTheJavelinMod before it loads this mod.
If you have still questions or something isn't clear just ask, I'm always happy to help.
