Orientation of BASE coordinate system

Hi,
is there a way to easily modify the orientation of the base coordinate system?
My use case is that I have an existing application (robot communicates with a host system, receiving and sending coordinates, joint angles, etc…). Now for mechanical reasons we need to rotate the robot base by 90degree. Is there a simple way to instruct the robot that robot base is rotated by 90degree?
I am thinking of a system settings (similar to the mounting configuration) where one can set the base system…

Volker

as there is no function for editing the base a solution would be defining a plane having the same orientation as the base coordinate system, setup the robot moving in the plane and rotate it on demand by editing the Rz param