As with any firmware type project, if the API doesn’t do what you want then use a different API.
Decawave provide the PANS positioning system as a pre-compiled and certified system. I’m guessing that is what you are using. This system is designed to be a generic positioning solution but isn’t very flexible outside that use case.
They also provide c libraries that can be used to access the radio chip more directly, this would allow you to use any message structure you like, change the data rate, change the power etc… This gives more flexibility but requires more knowledge of how the system is working and your end product will no longer be certified for sale unless you perform the testing yourself.
Or they provide the user manual for the chip and a number of application notes, between them they contain everything needed to write your own system from scratch. This gives the maximum possible flexibility and performance since you aren’t bound by any API or assumed structures. But it is also the most work and the highest risk since it’s all too easy to miss one little detail hidden away in the manual and end up with a system that doesn’t work as expected.
Power consumption doesn’t depend significantly on the data rate, it only depends on the time the transmitter is on. With a lower data rate the transmitter is on for longer.
The excel spreadsheet linked here: DW1000 Power Calculator not working can calculate the power consumption (and time) for a given packet size and speed.