[Solved] How does orientation work in S4S?

I can't explain it. But you might want to visit quaternions.online/ and check how to modify the 'orientation' in sims 4 which is a quaternion. The web page also shows the euler angels so you might use them to rotate the vector and then check the quaternion values.
You might either use the displayed values as is OR multiply the existing quaternion with the values displayed values and then normalize the quaternion.
Be aware that the web pages uses the WXYZ order with TS4 and S4S use XYZW, so when copying values from there just make sure that W is W, otherwise the result will be unexpected.

Avoid to use random numbers in the quaternion, w²+x²+y²+z² should always be '1' so you have a 'unit' quaternion.
w=1 and x=y=z=0 is the 'Identity' quaternion which you might see named like this in TS4. It means 'no rotation'.

This applies to all bones.

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You could of course also click on "Euler (XYZ)" in TS4 and enter there angle(? or rad?) values. There you might want to rotate around the X axis I assume. By just rotating +(/-) 20° it should be easy to see whether the rotate direction is the right one.