I was looking for a transform matrix to swap the x and z axis of rotation for something I am coding and I came across this useful page on Matrices: The Matrix Page

It's fairly concise and contains some useful info; including what I was looking for.

I'm fairly surprised that EE doesn't have a Transpose function(that I could find). Transpose would do exactly what you were looking for-swap the x and the z when used on a normalized Orn(3x3) matrix.
Matrices are amazing things.