Toggle Preset for TC/E in Preferences?

here you go. Just change the names of the plugin and presets.
The script will also make sure the correct TCE plugin is selected.

// Define TCE plugin
const tcePlugin = "Avid Time Shift"

// define presets
const preset1 = "Bass Monophonic";
const preset2 = "Guitar";

// define prefs window and open it
const prefsWindow = sf.ui.proTools.windows.whoseTitle.is("Pro Tools | Ultimate Preferences").first;

sf.ui.proTools.menuClick({
    menuPath: ["Pro Tools", "Preferences..."],
});

prefsWindow.elementWaitFor();

// Open Processing tab
prefsWindow.radioButtons.whoseTitle.is("Processing 6 of 9").first.elementClick();

// Select TCE plugin
//    check if desired plugin is selected and select it if necessary
const currentTCEPlugin = prefsWindow.groups.whoseTitle.is("TC/E").first
    .popupButtons.whoseDescription.is("").first.value.invalidate().value;

if (currentTCEPlugin != tcePlugin) {
    prefsWindow.groups.whoseTitle.is("TC/E").first.popupButtons.whoseDescription.is("").first.popupMenuSelect({
        menuPath: [tcePlugin],
    });
};

// get current preset
var currentTCEPreset = prefsWindow.groups.whoseTitle.is("TC/E").first
    .popupButtons.allItems[1].value.invalidate().value;


// Toggle Preset
prefsWindow.groups.whoseTitle.is("TC/E").first.popupButtons.allItems[1].popupMenuSelect({
    menuPath: (currentTCEPreset == preset1) ? [preset2] : [preset1]
});

// Close Prefs window
prefsWindow.buttons.whoseTitle.is("OK").first.elementClick();

the key part to toggling is this line:
menuPath: (currentTCEPreset == preset1) ? [preset2] : [preset1]

(currentTCEPreset == preset1) ? [preset2] : [preset1] is a ternary operator which is just a shorter way of writing if (currentTCEPreset == preset1) return preset2 else return preset1