Roll back to 10.2.3, 30-day trial, is possible!

James Cude, over on the Apple.co FCPX forum, posted this link to an Apple upgrade procedure document. There is a link in it to a trial copy of FCPX 10.2.

support.apple.com/en-us/HT202826

Before you update
When you update to Final Cut Pro X 10.1 – 10.2.3, your projects and events are updated. This article explains how your updated libraries and other files work in these newer versions of Final Cut Pro X.
Updated Final Cut Pro X files can't be used with Final Cut Pro X app versions earlier than 10.1. Before you update, create backups of the app and your files in case you need them later. You should also complete any active projects before you update.
If you're using Final Cut Pro X 10.0.9 or earlier and you want to update to Final Cut Pro X 10.3, you must first update your application to any version between 10.1 and 10.2.3. You can download and use the 30 day Final Cut Pro X 10.2.3 trial to update your Final Cut Pro X 10.0.9 or earlier projects and events to libraries and then update to Final Cut Pro X 10.3.