Snaps are squashfs images, which by definition are read-only. This can make them difficult to debug, since they cannot be edited. That's where this snap comes in. Run the following command:
$ /snap/overlay/current/overlay /snap/<name>/<version>
Now the snap can be edited! This is done via overlayfs, and it's temporary. One can undo it by rebooting, or by simply unmounting the overlay:
$ sudo umount /snap/<name>/<version>