could the Obsidian crystal get a secondary affect of if you try too apply it too a piece of gear that already has a crystal affix it can replace the prior affix with a new one

Only one crystal affix per gear

Yes of course but being able too replace them with another just by using another Obsidian would be nice for convenience sake instead of dicking around with quartz

-1 - If the devs wanted you to be able to change crystal affix, they would’ve implemented kyanite on it.