I've been curious aboutt this for some time.

The first thing I tried to do was to mess with the enable freestyle and 1-4 player thing under "Force Patterns" in the RGS editor.

However whenever I subsribed to the (private) mods I made for that in the workshop, I did not find them in the freestyle or multiplier menu when I launched Majesty to test them.

Today, I was using the editor's ability to load oringal quests from their file location

...steamapps/common/MajestyHD/QuestsMX

One of these is mx_Freestyle.q

Before I looked at this, I wasn't sure why workshop quests tagged with freestyle or multiplier never showed up in-game.

The editor documentation mentions that you can save multiple Force patterns, but there really isn't any reason to for normal map-making purposes. This quest makes use of this feature.

mx_Freestyle.q contains EVERY multiplayer and freestyle setting under it's Force Patterns
(and switching between them reveals the respective unit patterns, etc).

Conjecture follows -

I think that the template file arrangement of mx_Freestyle.q might be the reason why making multiplayer and Freestyle settings in the editor makes them show up (under downloadable quests in the singleplayer map screen or not at all) instead of in the freestyle and multiplayer menus.

If it's possible to create functional multiplayer and freestyle options at all with RGS, it likely can only be done by editing this specific quest file.

This should be possible without overriding the current options, since you can still add new force patterns to it in the editor.

I'll be trying this out myself more this week, but I'm hope this is useful to others
(or those better informed can correct my misinformation)