This example will use my implementation for Fort Fellhammer and assumes you have read the author guide.

First I made sure the keywords for FortFellhammerLocation included FTLoc and Clearable, and that it's parent was a vanilla hold.

I added three XMarkers outside the fort named FTMarker0_FortFellhammer, FTMarker1_FortFellhammer, and FTMarker2_FortFellhammer (the name is not required but helps differentiate them). I gave them the LRTs FTMarker0, FTMarker1, and FTMarker2 respectively. The marker0 is initially enabled while the others are initially disabled.

I set all 8 bandits to have the LRT FTFaction0. Their enable parent is FTMarker0_FortFellhammer.

I added 7 CWFortSoldierImperials with the FTFaction1 LRT. Their enable parent is FTMarker1_FortFellhammer. Their patrols and difficulty matched their bandit counterparts (not required, but I wanted it to be the same as the bandits). I also added 1 CWFortSoldierImperialCommander with the same settings as the soldiers and matching the bandit boss.

Same for the stormcloaks but with Sons instead of Imperial and faction2/marker2.

I also set the banners inside the baracks to have FTMarker0_FortFellhammer as the enable parent and added faction banners with their respective enable parents.

This is all you need in order to give an existing location the vanilla-like functionallity.