It might be possible, but setting a level for each week, especially considering the minimum level of 3 for a camp, probably won't work :(
Added 1 minute ago
I also need a selection of creatures of a specific level in the camp, which the camp won't allow (that's why I wrote about the idea of only 7 dwellings) and that's exactly what I meant by their replacement ;)
This can be bypassed with a script (and then the dwellings involved wouldn't be needed) - we give the level (or, more precisely, a set/list of creatures) that is needed according to the current week.