Well, what I am looking for is description of steps that one needs to do, if he would like to try fix something in e.g. system-settings.
You can just build new debs with crossbuilder,
Well, I can't get even through this step, since as mentioned in the first message,
crossbuilder just does not work for me.
push them to the device, make the rootfs r/w, and install the new specific debs (not all the binary packages that get built are necessarily installed). Or if there's a PR, CI will build debs in a repo, and you can use the
ubports-qatool on your device to upgrade the packages for a specific PR, to test. There's no need to rebuild and reflash the whole rootfs to test specific fixes.
Thanks for the story above, but at the moment stuff that seem to be so obvious to you does not make any sense to me... Need to do the first step - build something with
crossbuilder, then I will try to decipher the rest.