See Norikura Onsengo; English Poster on Hot Spring Etiquette - How to Enjoy the "Active and Slow Pace".
Okuhida Onsenkyo’s Spa Expert's pass ‘Yukemuri Tatsujin‘ program allows visitors to purchase a Spa Expert's Pass ‘Yumeguri Tegata’. The three bathing stickers attached to this 1,200 yen pass can be used to bathe at 2 - 3 of the affiliated hot spring facilities. See this Japanese site about details.
Day-trip bathing may not be possible at hot-springs with accommodation, depending on the season, time of day, accommodation situation, and infectious disease countermeasures. Please check with each facility in advance.