How to most easily save and re-apply a batch of tags from a data file?

Not quite - I described the steps in the previous post. I also described the conditions (most important: source and target files have to be in the same order as the data copied from the first file is then pasted to first of the target files, the data from the second source to the second of the target files and so on).
But yes: you could do it for several hundred files in one flow of select sources-copy-select targets-paste
In other words: you do not have to do it file by file and tag field by tag field but you can copy a whole tag and paste that whole tag to a target file
And that even works for a whole bunch of files in one go.
And the good thing: it also copies the embedded picture.