Re: Calendar type: 4-4-5, 4-5-4 or 5-4-4's restrictions
That makes sense. The breakback is the reason for your issue, it would let you enter data at the Month level through the UI, but not load data to that level since it would be the incorrect dimension based on the line item settings.
I would say your options would be to either change the dimensionality of your line items to set them to the Monthly level (which may not be possible if your business process requires entering data both weekly or monthly), or to build a second set of module(s) that mimic the current modules but with all line items set at the Monthly level, to which you would load your monthly data. You would then need some formulas to aggregate and pull down the data to the Weekly level if necessary.
Happy to provide more details on that, hope that helps!