Feature summary
https://commons.wikimedia.org/wiki/Special:UploadWizard
can the "copy information to all uploads" function add information rather than overwrite information?

Use case(s)
suppose you use uploadwizard to import these flickr images: https://www.flickr.com/photos/yann07/albums/72157719759878146 .
some photos already have descriptions, but some do not.
regardless, you want to add some descriptions to all photos. (it might be that you want to write in a language that's different from what all the existing descriptions are, like japanese.)
right now, if i do that, descriptions provided by me and copied to all uploads using the button, would erase all existing descriptions.
example: https://commons.wikimedia.org/wiki/File:Serena_swimsuit_by_Yann_C%C5%93uru.jpg i only realised its flickr description is "l'espiguette Gard" (which is the location of the photo, which is not geotagged) when i revisit the flickr page, so overwriting the description caused the loss of the location info. i overwrote the description with something useless ("woman") because another stupid design that does not allow an empty description field. (sorry for my language but this design caused all these troubles. if i could leave description fields empty then the flickr description wouldnt be overwritten.)
so, can the copy button please be additive only? or at least it gives some warning that it's overwriting something?

Benefits
the original descriptions at flickr often contain important details about the photo. it's important to preserve them, while utilising the copy function to add more descriptions.

this request is not only relevant to the description field, but also to categories, other information, etc. that can take multiple values (in contrast to fields, like title, date, that can only take a single value).