Gravity not correctly applied after a pysics.gravity rotation

I use

Physics.gravity =Quaternion.Euler(0, 0, -90) * Physics.gravity;

to rotate my gravities of 90 degrees. On my scene i have a cube in a closed area in a 2.5d setting (X,Y rotation and Z position frozen).

When i rotate the gravity the cube does not move, but if i check/uncheck Use Gravity in the rigidebody of my cube, he fall.

Is there a way to "restart" or "refresh" the gravity to really apply the gravity change.

Your cube might have fallen asleep. You might need to wake it up with Rigidbody.wakeup or with Rigidbody.AddForce (you can even add a force of zero to keep it awake).