to move the content of the dir you might be able to:
stop all snap apps ...
mv ~/snap /whereever/your/bigger/disk/is/mounted
mkdir ~/snap
sudo mount --bind /whereever/your/bigger/disk/is/mounted/snap ~/snap
you might need to adjust permissions on the target disk, the snap dir must be fully read/write for the user using it ... and can indeed create a systemd mount unit to make this permanent ...
to move the content of the dir you might be able to:
stop all snap apps ...
mv ~/snap /whereever/ your/bigger/ disk/is/ mounted your/bigger/ disk/is/ mounted/ snap ~/snap
mkdir ~/snap
sudo mount --bind /whereever/
you might need to adjust permissions on the target disk, the snap dir must be fully read/write for the user using it ... and can indeed create a systemd mount unit to make this permanent ...