Hello!

This tutorial will guide you towards making your memory card usable on any Vita without formatting, no matter the firmware. This is one time use and you will need to redo it for each time you want to swap. Be careful when transferring to firmwares without MailWriter.
Credit to HackInformer for the original method.

The only thing you need is a Vita with MailWriter set up, and Thunderbird. If you do not know how, check this guide. What we will do is format id.dat, a file which containts info linked to the memory card.

1. Download this .eml file.
2. Forward it to your Vita.
3. On your Vita, open the email, and upon getting the corrupted picture message press the PS button and close the email app completely.

You can now use this memory card on another Vita. This is one-use.