araksys64

If the internal storage has android installed then it doesn't needs to have a partition table. Multiple partitions show up in android because the partition offset and size is passed with kernel commandline, you can just backup the mmc as a raw image and restore it as it is anytime later.
Multitool or Armbian can't recognize the partitions of Android in this tvbox as they need a partition table to be present in the initial bytes else they treat the whole mmc as raw data.

You can backup the mmc using multitool script and on a pc or phone extract the resulting gz file. Then from this raw disk image you need to get the offset and size of the system partition and then use dd to get the system partition out. After that you can make changes to files in the raw partition image and write the whole image back to the same offset. Never tried something like this but if it is possible to get into recovery mode and try if adb over usb is available then editing the system partition would be easier.
The first method might worsen things so having the gz file saved at a safe place will be better