theoretically it would be possible to migrate the running system into an RPI5 compatible image and switch SD cards afterwards. For doing this, you would need to migrate to the new RPi firmware package Image | Raspberry Pi 5: Testing and firmware migration script 路 Issue #6676 路 MichaIng/DietPi 路 GitHub Keep an eye on the warning 
But we never tested the conversion from PRi2 into RPi5 system.