Depending on how the subreport is implemented, you may have some options. Subreports can be made either completely embedded in the parent report OR imported on opening of the parent file.
For example, open up a few of your parent reports and right-click on the subreport. Go into the sub-report's properties menu. If you see a re-import when opening option, then it's not embedded.
I'm not sure what your question is, exactly. If you are designing these reports and want to make a sort of Master/Template SubReport, then you should make it independently, import it into each report, and check the option to automatically re-import the subreport every time the main report is accessed. This way, you only have to update the 1 Master/Template SubReport and all the Parent Reports will be auto-updated next time they're opened.