Downgrade R17 to R13.1

Legato Linux distribution (Yocto project)
1

Module: WP7608
Background: some devices are in the field that are built with R13.1
My testing setup with the R17. I want to degrade to R13.1. I want to test the same scenario of the field device.

I tried the office version “WP76xx_Release13.1.1_GENERIC_GCF.exe”. but it could not downgraded.

how to wipeout all and flash R13.1.1

2

officially you cannot do so:
https://source.sierrawireless.com/resources/airprime/software/wp76xx/wp76xx-firmware-release-17/#sthash.N16iI5h9.dpbs