@tripplies we don't support third party installs, but to get the original games off you would need to transfer them off. see: https://retropie.org.uk/docs/Transferring-Roms/#transferring-roms. essentially you're doing the same process, but in the other direction. samba, SFTP or the manual copy would work. after that, install your new system on your new SD, and transfer them back in the same manner.
i would be reticent to transfer configs and the emulationstation setup as those settings are likely incompatible with current retropie and could cause issues/break it.