Developer's note:

Hey folks.

Here's a long promised Firmware-Pack (AddOn) for Recovery Flasher.

With this you can install 5.50-GEN-D3 directely with Recovery Flasher, no more need to first flash a M33 and then run the GEN installer, just hop directely to GEN - for those who want to.

Using is kinda easy, pick the .RFP file from the archive matching your PSP and copy it alongside the 550.PBP onto the root of your memstick.
In Recovery Flasher select "load from external FW pack" on the version selection, choose the Pack and off you go, it'll install the GEN then.

Needs Recovery Flasher 1.60.

Have fun