How to add tag to all images in 50k+ catalog at once?

I have a catalog of 50,000+ old (but still need to be retained) photos that I would like to tag as such so they don't get accidentally used inappropriately in new promotional efforts. But Lightroom cloud will only let me add a tag to 5,000 at once. Is there a way around this to get all 50k+ tagged at once? It's incredibly tedious to tag the first 5l, then try to find where the next 5k group begins.