I have saved a few templates in the "C:\users\[me😁]\AppData\Local\PTC\Mathcad Prime\My Templates", (basically the default template folder specified by the Mathcad app.) However, when I open one by the "Open -> From My Templates" command, it will load it and the name remains as the original file name and extension of the template file.
Most apps will protect your original template files by simply renaming the file to "untitled.[typical document extension]". This way, you cannot accidentally overwrite the original template file. In order to actually modify/update/tweak your original template file, you would need to rename the file back to the template file name in the template folder. Then in the same session you can tweak and save the template file as many times as you want. The renaming of the template to "untitled" only happens when you are loading a new document from a template file.
The problem arises when Mathcad does not operate similarly, nor protects your template files. When I load a template file and my typical MO is to get right in to writing equations and hitting Ctrl-S occasionally. Wammo, my template file is now overwritten. [cry, cry, cry]
An alternate method is to simply ask the user to immediately save the file as a new '.mcdx' when loaded, instead of renaming it "untitled.mcdx" and allowing the user to continue automatically. Personally I would rather not rename the 'untitled' document when first loading a template file but later on in the session when I get a better feel for the name I want to use. Sometimes I just want to load the template file and try write some scratch calculations that I was not going to save anyway. However, If it was forced on me I would accept it. Maybe it's only my bad habit to rename it later on and risk loosing my preliminary work if it was accidentally unsaved. It wouldn't be relevant if there was an autosave feature (which could even autosave 'untitled' documents.
Please, when loading a template file, have the app either (1) rename the template file to "untitled.mcdx" (or some other file name as you desire) or (2) force the user to save the file immediately, giving it a default filename of "untitled.mcdx" (or blank or something other than the original template name).