Yes. Uninstall OS 4.5 from your computer via the Control Panel in Windows. After it is uninstalled (leaving 4.2.2 on your computer), connect your BlackBerry and fire up the Desktop Manager. Go to the Application Updater and after it searches your device, you will see on the following screen, next to the software titles available for installation that it will Downgrade to 4.2.2. Continue and proceed, the DM will backup and restore your data appropriately.
"He that hath no sword, let him sell his garment and buy one."
Jesus, Luke 22:36
"The deadliest weapon in the world is a Marine and his rifle."
Gen. John Pershing, U.S. Army