How can the Param Get module read a value from a module higher up in the hierarchy?
You can add additional input pins (SysIn) in the subsystem module and use these input pins to control internal modules. Just connect whatever source you want to the new input of the subsystem module in the higher level design.
I think this will achieve your goal, but if not, please comment.
I'd like to avoid pins and the associated wiring, that approach in this design will make the schematic messy as it would go to a lot of places. I like clean, easy to read schematics. This value is kind of like a universal constant, it would be a global constant in code.
A single Param Get module that can read a value from a module higher up in the hierarchy is the cleanest way I can think of schematically.
In the Mod.Var parameter field inside your Param Get module, use a '\' character preceding the module name you wish to change. Every '\' you use will move you up one system level. This is documented in the param SET help file, which is available to you when you right click the ParamSET and click the "Help" button at the bottom of the list. We will update this to reflect the param GET module as well. Thanks for this find!