Given the current definition of `$:/core/ui/ViewTemplate/tags`, I don't see any other way to make this change without altering that shadow tiddler.
While this does add some extra steps to the upgrade process, upgrades typically only occur twice a year or so; and, when upgrading, the "status" column will indicate that you that you are overriding a shadow.
After upgrading, you can compare the modified tiddler with the default shadow using these steps:
1) Open $:/AdvancedSearch, Filter tab and select "Overridden shadow tiddlers" from the dropdown next to the input field.
2) Open `$:/core/ui/ViewTemplate/tags` from the search results and click on 'edit' to view the tiddler source
3) In the editor toolbar, enable preview (the closed eye) and from the preview options dropdown (chevron-down, next to the eye), select "differences from shadow (if any)"
The preview panel will now show the differences (if any) between your modified shadow and the newly upgraded shadow (red strikethroughs for removed content, green underlines for added content).
If the only difference is the change you previously made, then you're done.
Otherwise, you will need to delete your modified shadow and then edit the shadow again to hand-merge your changes into the upgraded shadow.
Sure, this is a bit of a hassle, but as I noted above, upgrades only occur twice a year, and most of the time, those changes are to core JS code, rather than UI definitions, so it's probably no more than a few minutes effort.