I wanted to know if we can change an os without removing the sd card. I basically have Gamepi20 and it is all locked up. there is no way to remove or add an sd card. I Don't have any mini cross wrench sleeves lying around, so unscrewing is not an option. I run a custom Retropie version which can be found below.
Retropie image: https://1drv.ms/u/s!At1XVmt1PVrlgSuwxNF-H3g1jsKg?e=Q01Ghv
Gamepi20 details: https://www.waveshare.com/wiki/GamePi20
You could boot from USB and reflash the SD card with a new image, then boot back from the SD card.
Make sure you don't overwrite the SD card with a corrupt image: if you reboot while the SD card doesn't have a readable boot partition (MBR, FAT32, with bootcode.bin, etc.) you won't be able to boot the system unless you take out the SD card and flash it correctly.
Your OS should have control of the Pi as early as possible so installing one on top of the other probably won't work as far as I know especially a custom install that will be configured for the machine's sole purpose of playing games and won't play well with anything else unless it's rolled back. I'm afraid that unscrewing the case is going to be the only option.
If you can overcome that hurdle then fit a micro SD card extender (available for a few $/£) and have the slot end taped or glued up somewhere out the way of your hands and that way you can swap out the cards as you choose.
