There was a technique mentioned in the Helmet Design video in ZClassroom, but I cannot recreate it, nor find the video, that does what I want, I think.
I have a curved surface and want to slice a circular polygroup into it. Just doing it distorts the circle; in the video the respective area that is to receive the slice was flattened, sliced and unclipped again. However, just clipping gives me no vertices to slice in the now flat area.
I havent seen the video in question, but there is a circular slice tool.
Hold down shift+Ctrl, and click on the brush menu, which will bring up all the selection/slicing/clipping/trimming tools. Select SliceCirc. Now when you hold down shift+ctrl, you will slice circular polygroups into existing ones.
Beyond this I would need to have more detailed info about what you want to do precisely.
However, just clipping gives me no vertices to slice in the now flat area.
You may need to remesh in between operations, either with dynamesh or one of Zbs other methods for doing so. Also consider using the trim brushes where you can (they dont work in every situation). These create new geometry when they flatten, not just distort verts which may then be unsuitable for other tasks.