The BT factor on the Gaussian pulse shaping filter is often used for narrowing spectral emissions at the Tx side to fit into a regulatory / applications standard mask requirement. On how to adjust the BT factor on the EZRadioPro familiy you can read here.
Note that adjusting the BT factor will only alter the spectrum emission of the modulated signal, it will not affect discrete spurious emissions that are not part of the modulation, like these.
Adjusting the BT factor, however does have an effect on sensitivity at the Rx side. This is quite often overlooked and may result in a huge loss in the link budget. To that end find below two graphs showing sensitivity versus BT factor parameterized with modulation index. (These measurements were taken on revision revB1B but hold up for revC2A/ A2A.)
Don’t ever go to a lower BT factor than 0.25 if the modulation index <= 2. If narrower emissions are required lower the modulation index instead.
Also be prepared that the frequency offset tolerance of the Rx degrades by dropping BT and / or the modulation index.