You can try using snap try with the .snap file to do this. First take the squashfs file built for that architecture from build.snapcraft.io and copy it to the device, then run unsquashfs <file>.snap and you will have a squashfs-root directory to work with. Running snap try squashfs-root will install the snap from that directory so all you need to do is modify the files in squashfs-root and those changes will show up in real-time in your snap to debug.