if it’s the same clip, just modified or improved but has identical length
it’s very easy and one of my main reasons to do my editing with fcp x :
right click on the clip you want to replace in the timeline and choose:
“open in timeline” (do in the time project timeline not in the event browser)
Drag your new / improved clip from the event browser onto the clip
in the new timeline, choose replace – et voila!
Click on the back arrow (top left on the tl window) and close this
temporary timeline and go back to your project.
All effects and settings (e.g. in/out) are applied also in your replaced clip too.
If these settings are obsolete because your new clip is improved you have
to delete them.
I use this very often if I want to replace a video clip by a graded version.
I dont have to do a xml roundtrip of a project to Resolve to grade a single clip.
Just grade one clip and bring it back to your project as described.
hope that helps