My 16' yurt sat on a very low platform.
This is how I accessed any point on the yurt roof. I'd take my 24' extension ladder and fully extend it. Then position it so the upper section was laying flat on the roof. Climb up and have at the work.
A bit of support stepping off with one foot or a knee out on a rafter is OK. My weight was mostly on the ladder, the foot or knee was for bracing while working. Standing with full weight on 1x3 rafters ain't gonna happen.
I tested my 1x3 rafter strength by hanging from two adjacent rafters mid span inside the yurt. No problem with holding my 210 pounds. But that was inside not out.
If I regularly climbed up there and crawled or walked around servicing the
or stack or whatnot, on a yurt that was 20' diameter or more, and with a tighter rafter spacing/size and interior support poles, I just might have a different opinion.
That's all I got. Good luck.