So Question is Has anyone tried to change the speed? Is it possible somehow to tell Bitcloud not to change values?
It is impossible and very wrong.
2 Mbps data rate comes with limitations on how LQI and RSSI values are calculated. And they basically will be very inaccurate.
BitCloud relies on those values to maintain mesh network topology. There are also a whole lot of constants calculated based on 250 kbps timings. All those things will also be off, and it is hard to tell how that will affect network performance.
If you want to go proprietary, use LwMesh and do whatever you want with the transceiver. LwMesh will still use LQI, which will be invalid, but at least you can introduce a different link quality metric, if you really need.