Will empty exif presets overwrite existing exif data (like captions) with blanks

Question

I want to import from existing files and keep whatever exif data is already there (like captions), while during the import (or after) I want to apply ADDITIONAL exif data (like author, location). If I leave the existing fields empty in the metadata presets, will the original exif data be safe? In other words, can i just append metadata without affecting the original values?
DJ

Answer 1

In the Edit Metadata Preset dialog (where you would name and save a metadata preset FROM), there are checkboxes down the right side, next to each metadata field.
Any field without a checkbox next to it, will be left alone when the preset is applied to future images, regardless whether there is something typed into the preset or not, and regardless whether that field on the image starts out empty or not.
This is the same idea, as with Develop presets: the preset has a defined scope. It only affects the aspects that you say it should.
Typing something new into an empty box, does automatically put a check next to that.  So that will get applied to the image.
Editing out what is in a box, still leaves that field checked. Alternatively, you can put a check next to an empty box: same result. As a warning, that field's name turns red and the box shows a prompt telling you that if applied to an image, this empty field will still be imposed onto the image - deleting whatever might have been there before.
In order to prevent this happening, assuming you didn't positively want that field cleared, you would need to un-check the box next to that field (and then if editing a previously saved preset, update that to incorporate the change).