Yes , and no ;-)
With RAPID virtually anything is possible, question is what you want to do and how you want to do it.
There isn't a predefined instruction for what you want to do but there's nothing preventing you from doing it.MoveAbsJ is the instruction to move use for moving the robot to specific joint targets.CJointT is the function you want to use to capture the current position but in angular format.
Programming it this way is really cumbersome and kind of defeats the whole purpose of a coordinate systembut if you want to use the existing position and just move one axis a certain number of degrees it's definitely possibleusing the instructions I just mentioned.
to change axis 5 to 15° as below: