It took work, but I was able to keep Golden Farrow at 25% tax rate for a long long time. I had to stay in the region, but so long as I stayed in Golden Farrow I could keep it at 25%
I was a high skilled priestess and an ambassador plus I was ruler. So I got ruler bonus while being in the region and I could use priest skills to increase morale and ambassador skills for increasing loyalty. Then whenever I had to increase control I would throw in a harsh court.
In other words, you could do it but you were an exception not the rule, and even then it took plenty of work.
