I think one inefficient way to do this would be with variables and String.Contains. But that would require you to change your format so there would be a way to identify which number is which and you'd need hundreds of lines....
xml:
<variable name="File_Size">
<value condition="String.Contains(ListItem.filename,FileSize.50.3G)">50.3G</value>
<value condition="String.Contains(ListItem.filename,FileSize.50.2G)">50.2G</value>
<value condition="String.Contains(ListItem.filename,FileSize.50.1G)">50.1G</value>
...
You could make it easier by rounding your filenames to the nearest GB if you didn't want to do every decimal. But again, that would involve renaming your files.
The bigger problem with this is that it's non standard info typically not included in filename formats so if you were doing this for other people to be able to use, it's dead in the water.
If this is just a personal mod, you might be able to get away with editing your .nfo XML files and using a field you don't need that Kodi can read from, then just putting the info you want Kodi to show in there.
Again, not a great solution and probably terrible advice, but at least viable for a personal mod. With combination nfos you can even stop scrapers from overriding just these fields that you manually enter
https://kodi.wiki/view/NFO_files/Combination
This is one of mine where I wanted to control MPAA, studio and set, but for the scraper to do the rest. You just put the direct tmdb link after the </movie> tag
xml:
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<movie>
<sorttitle>Spider-Man 8</sorttitle>
<mpaa>12A</mpaa>
<playcount>1</playcount>
<lastplayed>2022-3-26</lastplayed>
<set>
<name>Marvel Cinematic Universe, Phase 4</name>
</set>
<studio>Columbia Pictures</studio>
</movie>
https://www.themoviedb.org/movie/634649-...o-way-home
Either way, it's going to be a lot of work to do it.
I would also have a look at your video files if ListItem.size isn't working. That should work.