I have a master page which is being inherited to sub-sites as well in our SharePoint 2016 site collection. Now I got a requirement for a sub-site which should have a different header other than its top level site. I updated the master page and set it as default master page from SharePoint designer but it is not getting replicated. Is there a way to change the header so that it won't replicate my top level masterpage to my sub site.
I have done it finally. Created a blank master page (e.g new.master) from the SharePoint Designer 2013 and then pasted the master page code of Top level site in to the new master page. Turned off the publishing feature from sub-site. Then from the s4-notdlg change the banner referring to the Site Assets where I have stored my image as shown below.
<div id="pea-header" class="s4-notdlg"> <img src="/sites/topsite/subsite/Site%20Assets/bannerDP.png" alt="" width="100%" style="text-align:center" /> </div>
Then Right click on the new.master from designer and make as Default master page and Custom master page.
Viola! done I can see my banner for just sub-site has been changed. Hope it helps others who come across this.