OmegaT 6.0.1 manual explains
https://omegat.sourceforge.io/manual-standard/en/chapter.windows.and.dialogs.html
Use this button to create local rules specific to your project. Check the Use local segmentation rules box, and adjust the segmentation rules as desired.
The project will store the new set of rules in the segmentation.conf file located in its omegat folder. These rules will supersede the global segmentation rules.
OmegaT 6.x will save segmentation.srx
instead of segmentation.conf
Do you mean starting from 6.1?
Done in docfix branch.
https://github.com/omegat-org/omegat/pull/1266
https://github.com/omegat-org/omegat/pull/1266