Hello,
We published a documentation on how to convert a mono-sandbox platform [1] to a multi-sandbox one [2] on our GitHub account [3].
The MicroEJ Team,
[1] https://developer.microej.com/glossary.html#microejsinglefirmware
[2] https://developer.microej.com/glossary.html#microejmultifirmware
[3] https://github.com/MicroEJ/How-To/tree/master/Single-App-to-Multi-App-Platform