Sounds like the sort of questions I'd find complicated too.
Going back to the original question...
kerravon wrote:
If I have a PC with a bios it will then think that this is an external hard drive and mount it and even boot from it.
This will enable me to transfer data between pdos running on the PC and pdos running on the Android.
You could use the same image for an emulated or virtual PC on the real PC. Perhaps the guest could have access to a partition in addition to the Android-hosted disk image. Make the PC dual-boot, with the other OS being PDOS accessing the partition. I made a plain-text diagram of this; just felt like it.
Code:
+--Android--+ +--PC--------------------+
| | | WinLinWhatever |
| | | +--VM-----+ |
| | | |PDOS | |
| | | | | |
| DiskImage-+---MTP---+-+ ↔files↔ +-PartitionN |
| | | | | |
| | | +---------+ |
| | | |
+-----------+ +------------------------+
Reboot PC...
+--PC----------------+
| PDOS on PartitionN |
| |
+--------------------+
As for the 2nd question, I'm sure you could use mtools under Termux or under any of the many Linux chroot environments you can get for Android.
Honestly, for the first question, you could use mtools on the MTP-served disk image instead of running a PDOS VM.
EDIT: Today I tried to edit a text file shared over MTP, but it wouldn't save to the phone. I guess you may not be able to write to the disk image served from the phone. So many useful things in Android require root access, and I can often understand why. What I don't understand is why I myself haven't rooted every Android phone I've ever owned.