Is it OK to use MacOS Laz IDE 2.0.10 and 2.1 on same code?
Yes, provided that for Lazarus 2.10 you:
* tick Project Options > Miscellaneous - Maximise compatibility of project files (LPI and LPS) I have no problems swapping between the two; and
* specify a different .lazarus directory (eg open ~/lazarus-src/lazarus.app --args "--pcp=~/.laz_trunk").