I agree that "historic=bridge_site" makes more sense than "historic=bridge site", but when you're changing tags like this it would make sense to contact people who are actually consuming the data.
In this case, if you go to https://taginfo.openstreetmap.org/tags/historic=bridge%20site#projects you'll see a link to https://taginfo.openstreetmap.org/projects/someoneelse_style and from there to a github project where you can create an issue.