Ok, work well om a VM and my next step is to test on a real machine (backup NAS so no problem if something goes wrong).
Usefull link to know selectable types of MergerFS (Policy descriptions) : https://github.com/trapexit/mergerfs
My first surprise, once I update plugin My AUFS pool dissapear from mhdfs/AUFS (union Filesystem) so I can't delete it, is still working but I can't destroy AUFS pool to recreate as MergerFS.
Of course , i Previosly deleted all references to BPool to avoid delete of it (Bpool is my Video Pool)
PD: Is not possible to delete from Sistema de Archivos, only form Union Filesystem, and as you can see, when upgrade plugin, is blank.
Do not worry, I still continue, only need to edit by hand fstab and openmediavault.xml config file to delete all references to my AUFS Bpool