Signature change problem

I had mapped out a I piano piece, which is very involved with many time signatures, and tempo changes, and thought it was as desired when I realized one measure was better interpreted in a simpler way. I have as 5/2 and there are polyrhythms that really don’t match up well any beat, though it sounds right. It would be better interpreted as 15/8 as then one line is just 5 groups of three eighths notes. so I first tried to do it changing the time signature , and this affected all subsequent measures. I started rewarping, but after I got about 4 measures, one was crushed at 360bmp, and I couldn’t change the next to unaffect this… There are over a hundred measures following. I then saw about process bars on another of my threads and thought this was the solution, but I wound up with the same result as the manual method. I haven’t thought of any solution.