I have created a sub site and I define a custom master page for it. Then I save it as a template. After that I started creating sub sites based on the template, where all the subsites get the custom master page as defined in the template.
Now let say I have 20 sub sites , and I want to do a change to all the sub sites master pages such as changing the footer or the search box location. Currently each of the 20 sub site have a separate master page and to apply such a change I will need to modify the related 20 master pages separately. Now since I will always need the same master page to be used inside all the subsites including any future changes , so is there a way in SP to force the sub sites to be using the same master page (shared master page) , so if I modify the shared master page it will affect all the sub sites at once ? Thanks