How can the device orientation be set?

[dougbert-b]

This can apparently be done by writing a FRS record, but the API does not provide a way to do this.
There is some FRS-related code in SparkFun_BNO08x_Arduino_Library.cpp, but it is commented-out, and I can't tell if it was commented out because it was unneeded, or because it no longer worked...

[LazaroFilm]

You could rotate your quaternion. https://www.euclideanspace.com/maths/geometry/rotations/conversions/eulerToQuaternion/steps/index.htm

[dougbert-b]

I ended up simply calling sh2_setReorientation() at startup, passing in the quaternion that describes the desired orientation.
Probably this data could be written to the BNO085 flash memory, but it is no big deal to set the parameters at each startup.