Is this really correct? You do a copy of FS to Kernel of SLOT A and the similar to SLOT B.
I would expect to copy FS from SLOT B to FS SLOT A and the same for Kernel.
And this leads to
dd if=/dev/sda3 of=/dev/sda2
dd if=/dev/sda5 of=/dev/sda4
Maybe I’m wrong, because I’m not familiar with Linux.