a half-dozen times over the years, and it only turned out to be a positive experience once. I was visiting my current favorite at the time and when our session was finished, as I was dressing, she went and got her roommate and brought her in and introduced her to me, telling me that they were offering doubles sessions. I took this to be a green-light to see the roommate, but just to make sure, a few days later I booked an hour doubles session, with an hour with my favorite immediately after, so after the double, the roommate would simply exit the room and I would do round two with my fave.
The reason for this was exactly what you suggest. I had never had a back to back of roommates that didn't result in a cold shoulder the next time from my regular, so I booked the second hour alone to handle any damage control and reconfirm for her that she was still my number one girl. It went very well and was glad I did it.
I tried a few more back to backs after that and had them turn out poorly, so now when a booker tells me he's got some new talent starting the next day, I ask who she is rooming with. If its a girl I have been seeing regularly, then I pass until the week my regular is off for her period. Have never had blowback doing it like this. The Kgirl mentality is that if I'm available to see someone, and they are available, they are insulted if I don't see them, but if they are on vacation and could not have gotten my business that week anyway, then they are not bothered that I got my pussy fix from someone else, even if it was her roommate.
To finish with my example above, when my regular decided to return to Korea, she brought her roommate in again and told me that I should see her regularly because she had told her roommate what I like and what I don't like and she will take good care of me going forward. It was an extraordinarily seamless transition and kept the roommate in my rotation for over a year.