Options in the fabric.mod.json - ModManagerMC/ModManager GitHub Wiki

Setting the Modrinth id

Mod Manager now allows you to set the project id manually:

Just add the following to your fabric.mod.json:

"custom": {
    "modmanager": {
        "modrinth": "myProjectId"
    }
}

Disabling update checks

Some mods may implement a custom updating program and don't want ModManager to check for updates.

This can be done by setting a value in fabric.mod.json:

"custom": {
    "modmanager": {
        "disable-checking": true
    }
}