Applying White Balance for Multiple Photos

Hi,
I'm new to FRV, ver 2.0.7, and I've been really enjoying it so far as it is genuinely *very* fast.
I have one question about white balance that was asked in 2016, but doesn't appear to have an answer: how to apply a custom WB to an xmp file for > 1 file.
To start with, these are my settings Image Display > White Balance (see attached if not displayed):


So, when I open a photo and type in a custom WB level, I see that an xmp file is created with the appropriate value for WB, and when I use the arrow keys to move to the next/previous photo, the custom WB level is applied to the photo, but the custom WB is not written a new xmp file, or an existing XMP file for the image is not updated.
While I like being able to view the same custom WB as I go through the images, how can I apply the same custom WB to numerous photos such that it's saved to the xmp file?
Thank you for your help!