Tutorial: Manually creating a settings class
You will need the template mod that ships with the LE1 Community Patch to manually create a new submenu. If you already have a menu set up and are just adding a new one to the same settings file, you may be able to get away with just creating a new class from class compiler.
Each submenu will be it's own class, a subclass of the ModSettingsSubmenu class that is shipped with LE1CP. Clone over the ModSettingsSubmenu_Template class from the template mod into your submenu PCC using the Clone all References option. Extra data getting pulled over is expected, this can be safely ignored.
The submenu class name must be globally unique. The easiest way to rename it is by renaming the class in script editor and clicking 'Compile'. Alternatively you can rename both the class and it's defaults object in the Metadata tab. You should name the class something to do with your mod, or which submenu it will be.
A new file with custom submenu set up. The exports nested under export 1 are what get cloned over, exports 77 and 78 are the custom submenu for this mod.
Your new submenu class now must be installed into the settings menu framework to show up in the "top level" of submenus. You may skip this step if your submenu will be accessed from within another menu you are working on.
This step happens entirely within a text editor, using the new M3CD Coalesced Delta feature of the ME3Tweaks Mod Manager. Please read the tutorial on that feature for more details of how to set it up.
Add the following section to your .M3CD file to install your submenu into the top level settings menu:
[BioUI.ini ModSettings_Submenus_LE1CP.ModSettingsSubmenu_Root]
+menuItems=(srCenterText=78888723, srDescriptionTitleText=78888724, srDescriptionText=78888725, Images=("GUI_MOD_TemplateMod.Images_Example"), SubmenuClassName="TemplateMod_ModSettingsSubmenus.ModSettingsSubmenu_MySuperCoolMod")