This guide is for the Epson Printers and should work on any model from 300 through at least LQ830, and likely many others with minor adjustments in the instructions.
1. Connect a USB Printer cable from the back of your printer to a computer or laptop. You must use a Type A/B printer cable and plug it into the correct USB port on the printer (square) not the standard USB input port on the front. When in recovery mode, a USB connection is required to transfer the firmware to the printer, even if you already have it connected wireless.
2. Remove all of the ink cartridges from the printer. This will ensure that all cartridge-related errors will be reset after applying the alternate firmware.
3. Power off the printer. As soon as the printer is completely shut down, perform the following key combination until the firmware update screen appears in white text [if the printer instead boots to its regular screen or IPL mode with red text, you may have to look-up or experiment to find the proper recovery mode combination for your printer model]:
4. For many series from XP-300 to XP-630: Press and hold the STOP button, LEFT ARROW button, HOME button and POWER button simultaneously
5. For the XP-440 to XP-446 and XP-640 to XP-646: Press and hold the STOP button, LEFT ARROW button, DOWN ARROW button and POWER button simultaneously (thanks to Ken for the combo)
6. For the XP-800 to XP-830 and similar single button models: Press and hold the TOP-RIGHT corner of the TOUCH SCREEN and POWER button simultaneously.
7. For other models or if you can't get the above to work: Try all of the above and if you still fail to reach recovery mode, you can search for additional combo keys.
8. Download the older firmware onto the connected laptop or computer. For your convenience, a table containing older firmware for the most common printer models is available below. If you have a different model, it may take some research to find the desired firmware since most printer manufacturers remove obsolete firmware from their site immediately and provide no downgrade instructions. Epson's printers use a self-installing firmware updater that can be run directly from Windows or MacOS.
9. After launching the downloaded firmware installer, step through the wizard by following the on-screen instructions. In the case of Epson, you mostly have to click next through a few pages of disclaimers. Assuming the printer is connected to the PC with a USB cable and powered up to the recovery screen, you should see a single entry in the Model list and it should be checked. Click Start to begin the firmware downgrade, and then click Yes to confirm. The prior firmware will be transferred to the printer, where it will begin flashing automatically. This process can take several minutes, but when it is completed the on-screen display will indicate that it has finished.
10. Once the downgrade is complete, press OK or unplug the printer to power it off. Then power it on again. When prompted, insert the ink as usual and then let the printer complete the ink initialization.
This way you can easily downgrade the firmware of the Epson Printer.