can they do this ? how would you like....

You say you're working in a "small private facility". Are you in fact members of a union? If you are members, then you should have a copy of the collective agreement, or access to one. Have a look at the collective agreement for the article that relates to hours of work and scheduling. It's usually near the beginning of the agreement. That article should contain the "rules" for scheduling, including provisions for master rotations and changing master rotations. Be aware that these articles may be subject to alteration within the context of "local conditions" that would be found in the latter half of the agreement. If you find that your employer isn't following the terms of the agreement then your union could and should help you. If you need help interpreting what your collective agreement says, I'll be happy to help you with that.

If you're not actually members of the union, then there's not much you can do, except make your opinion known and perhaps find a new job.

I know exactly how you feel. My unit will be starting on a new master rotation tomorrow. The rotation I had before was perfect for my needs and I was very upset to discover that none of the lines for my FTE looked even remotely like it. We also have the choice of self-scheduling, but in reality it's more a case of you indicate when you want to work and they'll tell you if that's okay. I felt coerced into agreeing to self-scheduling by the absolutely unbalanced lines I was offered, just so that I could have a semblance of stability. I plugged my existing rotation into the staffing matrix and negotiated in good faith to adjust my schedule to balance the numbers when the time came. Then the schedule came out, and there had been 8 more changes made. There is no possibility of stability or predictability with self-scheduling. And we schedule so far in advance that it's almost comical. This new rotation comes into effect with 3 1/2 months of the vacation year still to come. People who booked their vacations based on their old rotation have found themselves in a situation where the self-scheduling committee has changed their selected shifts and now they're going to have to use more shifts than they have banked in order to take their previously alloted vacation. That is NOT fair, to force someone to "borrow" vacation hours from the next year. There are a number of grievances ongoing over that.

The BCNU provincial agreement doesn't have nay specific reference to how or when a master rotation may be altered. I think you're going to have to get your local involved.