Answer:
Yes, it is. You can do it.
If you activate the option to create combinations automatically in RFEM or RSTAB, load combinations for the "ULS" design situation, for example, are set automatically according to the second-order analysis.
This way, you can obtain a list of load combinations based on the defined load cases, which are calculated according to the second-order analysis. The consideration of imperfection load cases can also be activated.
To generate the load combinations according to the geometrically linear analysis (without imperfections), in addition to the existing load combinations calculated according to the second-order analysis (including imperfection), you can create another combination expression. In this additional combination, you can now select the "ULS" design situation. However, you can only select the "geometrically linear analysis" as a method of analysis and deselect the imperfection load cases.
As a result, you obtain the load combinations according to the second-order analysis including imperfection (marked in blue in the image below) and the load combinations according to the geometrically linear analysis without imperfection (marked in red in the image below).
This approach can be used to perform the stability analysis according to the second-order analysis (including imperfection) on a part of the structure and according to the equivalent member method or model column method on the individual structural components, for example.
Optionally, it is also possible to control the numbering of the individual CO groups in advance in the "Combination Expressions" tab. For example, one group can start with CO 100 and the second group with CO 200. This way, you can achieve a better overview or better allocation of the COs.