Removing a KNOWN VBA password via VBA

So you would put all the code in all the files in a read only add in?

Yes.

We have 1000s of file and its quite common for them to have upwards of 20 modules.
I feel like an add in with literally 10000s of modules and forms ...

Huh? Workbook A has 20 modules, and they are all different than the 20 in Workbook B, and all different than the 20 in Workbook C, and ...???

... would be very very difficult to manage

How well are you managing with your current approach?