Hi, I don't think it's possible to save a template to a file without completing the variable. As in your example, if you use the {person} variable in a caption and the person shown field is blank, you'll end up with a gap in your caption.
There are several workflows I would suggest, depending on the job.
If it were a job photographing a large number of speakers at a conference where I had all the names in advance, I would create folders for each speaker, then use Hot Codes to add captions, the person shown, and keywords, etc. I create folders on my computer, but Jeff Vogan has promoted a very clever way to create folders in the camera.
https://www.youtube.com/@jeffvoganphotographyOtherwise, you could just reapply the template with the person shown added.