apparently the program provides for the display of barcodes and вisambiguations in some cases. it would be cool to have some kind of customization of this behavior, or at least a plugin to do it
No that’s currently not possible. There are some tickets to show more information in this selection (PICARD-964, PICARD-2010). But as this display already does not really work well when a lot of information is being displayed we are considering to change this to a dialog instead, which would allow to display all this and more information, see also PICARD-966. In the current display as a submenu it is not really feasible to add more information.
I really have no idea whether edits to Musicbrainz to add (literally) a hundred odd countries individually in order to omit the few countries where it was not released is better than using XW to show a worldwide release. But it certainly looks awful and is extremely unhelpful as we can see from the image above.
Given that the country code is so unhelpful when they are like this (as an aside, should the country codes be sorted before display so that the differences are more obvious - and so that the list in consistent regardless of the sequence they are sent in), the barcode and disambiguation would certainly seem to be more helpful in these situations.
Actually this is the key here, and this can actually be considered a bug. Usually this should already show barcode and disambiguation, but I think it doesn’t because displayed countries are all different. Also it probably should just display some hint that these are a lot of countries instead of this partial list
Perhaps Picard could say “XW except RU+ZW” or similar if there are only a few countries missing from the list or “Many countries” if the list is too long.