Originally Posted by
Augustusng
This mechanic is located in a script, in data.pack, under campaigns -> main_attila -> sands -> military_building_locking.lua.
You can adjust the numbers there; you should see lines in that script for each of the level 5 buildings, with the "75" number. You can change that number; that's the easiest way to do it.
But... you also have to change the text file, so the message displayed when you mouse over the building is different. That's located in your localization pack. In the English version, it's under campaign_localised_strings.loc. The lines you want to change start with *building_restriction.