I was using WP7605 with Rev13.3.1, but after upgrading to Rev.17, some functions stopped working. I’d like to revert back to Rev.13.3.1. Could you please tell me how to do that?
no, you cannot do that, it is stated in the firmware release page:
https://source.sierrawireless.com/resources/airprime/software/wp76xx/wp76xx-firmware-release-17/#sthash.BxSMGpuN.dpbs