Movie project in ACES from HDR PQ to DCI

Yeah that is the Dolby secret sauce to adjust image and trim levels for lots of outputs and embedding them in the master.

But if you are just doing an HDR grade and then wanting to make a P3 version in practical terms it works the same with the Dolby analysis. The output transforms for each display type do work pretty well. If you make an adjustment to make HDR look like you want it usually still is close in SDR.