I changed the fortification level of town_EN6 in my mod's settlements.xml to 1, however in game the walls were still level 3. The only way I can see level 1 walls in game while testing my worldmap is to edit settlements.xml in the sandbox module. Clearly, the game engine is taking name changes from my settlements.xml but ignoring it for level changes to towns. Cross checked by a colleague on another mod who experienced the same problem. Seems levels can be changed on castles in a mod's settlements.xml but town changes are ignored. Tests were conducted on sandbox, not story-mode. Hopefully this is an oversight, which you can fix.