How to do RTCP jog rotation around an axis in a TP program?

For our application, we need to rotate the robot around the Y-axis of a defined user frame. When I use RTCP jog around the Y-axis (of a user frame), this rotates around it just as expected. I am unsure how to achieve this behaviour in a TP program where I would have to specify a target position. What I would like is to have a movement command that represents "RTCP rotation around Y-axis in a specified user frame by a degrees". Is this possible?

As a note, we currently implemented this by defining an RTCP frame that is identical in orientation to the user frame, but the origin is located at the RTCP. Then we take the robot's current position in the RTCP frame with LPOS (call this position P1). Subsequently, the RTCP frame is rotated around the (world's) Y-axis by the desired rotation angle, and when P1 is now expressed in the new frame, it represents the rotated target point P1'. Only thing is, the rotation of the RTCP frame is done around the world's axis if I understand correctly (extrinsic XYZ Euler angles right?). In most of our applications, the user frame's Y-axis is parallel enough with the world Y-axis to not cause trouble, but I expect this could come back to bite me in the future so I wish to find some alternative method (that doesn't include trigonometry preferably).

Won't a tool offset always be relative to the tool's axes? Because I require a rotation about the frame's Y-axis, which may not necessarily align with any of the tool's axes.

Edit: just tested it and indeed this uses the tool frame. I could use a regular offset which will be in the current frame, but like I stated that would require some trigonometry (for the position) which I am trying to avoid.