If you share the property extension like any extension, I remember you that it shares all the records of the extension.
This mean that SiteA, SiteB and Master C will see the same records and can update any records.
It is not possible to select which website manage which records.
JMS does NOT change the extension table.
The concept of the extension sharing is to share the MySQL table and therefore all the records.
Therefore you either decide to keep the com_properties specific to each slave site or to share ALL its records.
Acheive this kind of objective require to modify this com_properties extension to make a "multisites com_properties".
If you want that we develop such extension, you can order our billable support that can also be used for specific development.
www.jms2win.com/download?page=shop.produ...35&category_id=1
This probably require several days of support.