Answer:
Yes, this is possible in RFEM. However, you have to disconnect the generated load first. The generated loads are then converted into normal member loads and can be changed as required.
After disconnecting the generated loads, you can define the load eccentricity.
As expected, the member loads generate a torsional moment if they act eccentrically to the shear center.
The options for RSTAB are described in FAQ 2361:
FAQ 002361 | Considerating Eccentric Load Introduction