Possible to Downgrade Firmware on XFfinity XFi Routers?

Many of our users work from home via an Ubuntu based thin client. The vendor we use to configure these devices advised that the latest firmware update pushed to some XFinity routers, CGM4140COM_4.4p8s1_PROD_sey, appears to have broken the ability of the vendor's devices to connect to the user's home wireless network. They advised, if possible, downgrading the firmware to GCM4140COM_4.6p7s1_PROD_sey. Is there a way for home users who subscribe to Xfinity XFi, and rent a router from Comcast to do this? Please note that our vendor is actively investigating why the firmware update broke the product, but in the interim, are unsure of what to do.