Sharing between Hacked and Unhacked Vitas

Background info:

On the memory card of a Vita there's a file called id.dat. This file contains the name of the PSN account the memory card is linked to, and the firmware of the last Vita it was used on.
If you use the memory card on a 3.61 Vita then id.dat will reflect that. If you take that card and put it in a hackable 3.60 Vita, the Vita will refuse to use the memory card without formatting it first.
To get around Sony's "feature" you must place the 3.60 console in IDU mode, where the id.dat file is ignored. Then you can delete the file and let the 3.60 console generate a new one. You can then make the file read-only, so it won't be updated when it's put in the 3.61 console.
From that point onward you can freely swap the memory card between the two consoles if they are both linked to the same PSN account, until the id.dat file is somehow made read-write again.

The guide assumes you have HENkaku and know how to install .vpk files.

Deleting a 3.61 id.dat:

- Install Vita IDU on your 3.60 Vita. You can get it here.
https://github.com/xyzz/vita-idu/releases
- Note the warnings. Disable wifi on your Vita and try not to turn it back on while in IDU mode. It will try to auto update. Set up HENKaku's offline installer if you don't have it already.
- Run the newly installed vpk and set your Vita to IDU mode. Turn wifi off and remove the ethernet cable if it's a PSTV, then poweroff.
- Insert the memory card from the 3.61 Vita.
- Power the console on.
- Hold R + L + Up + Start for a few seconds to leave the demo mode sandbox.
- Launch HENkaku. Try to use the offline exploit, but if that doesn't work then you can survive a minute or two trying to use the regular online version.
- Delete the file id.dat in ux0:
- Open vita-idu and disable IDU mode.
- Reboot the console with the memory card still in
- A new id.dat will automatically and silently be generated.

Making the 3.60 id.dat read-only

- Install memcardswap on your Vita
https://github.com/SMOKE5/memcardswap/releases
- Set your id.dat to be read only
- Done!

What now?

- You can swap the memory card freely between your 3.61 and 3.60 Vita. 3.61 digital games can't be run on the 3.60 Vita this way.
- You can install game mods as patches (undubs, uncensors) with Major_Tom's trick on the 3.60 Vita, and then run them on the 3.61 Vita.
- You can install VHBL on the 3.60 Vita. When you swap the memory card to the 3.61 Vita VHBL will still be working. You can then run a selection of PSP emulators on your 3.61 Vita.
- You can't install pirated games or Vita-mode homebrew on the 3.60 Vita and transfer them to the 3.61 Vita this way.