How can I get Final Cut Pro to reload my Motion projects without restarting it?
Hey Peeja… the "official" way is to simply REPLACE the title or whatever in the timeline with the original from the browser. Select in the timeline, then select in the browser and hit ⌥R to "Replace from Start". Or drag from the browser ontop of the timeline instance and select replace from the pop-up.

It's because the edited version only exists in the browser and the instance in the timeline is independent of it.

The UNofficial/Power User way … simply CUT the title or whatever from the timeline and… PASTE. Done.  

Cheers.