Yes. We can do that.
You can develop a small application in the PC to send a specific vendor command (let say Cmd_to_Erase) to FX3.
Your application firmware should be supporting this command. When FX3 gets the required vendor commad then do erase the signature of the image file that is stored in the SPI EEPROM. And when the end user hits the reset (disconnect and connect it back) then FX3 bootloader falls back to USB since there is some invalid image in the SPI EEPROM. Then user can re-program it.
thanks for your reply. That's a good idea and i will try it that way.
If you implement a vendor comand to erase the first bytes of SPI flash, you can implement the whole code to erase all the flash content and write the new firmware image to the flash. I think this is only a very litte more work...
Yes you are right. Thank you.