Because changing the file’s icon changes the modified date (as perhaps changing other attributes does as well), is there a way to see (and work with) files’ actual contents’ modified date?
I think this may be a bug in fact, taking a look at how the Mac version handles it. Indeed metadata changes (like updating the label) are considered a form of modification, and generally this is desirable as you would want such workflow level changes to be sorted in the outliner and such. But the custom icon has always been a bit outside of metadata. It isn’t really treated as such (there is no search or sort function for them), and they are largely cosmetic. It would be a lot more like “Convert to Folder|File” (which I note also incorrectly triggers a modification update).
So I’ll make sure we have a ticket on this.