label the processString with _gen for generator specific relvals

- back port from 7_3, the same logic as pr #6104
- only relevant for submission to computing; not relevant for performance / IB
- label the processString with _gen for generator specific relvals
- as requested by @anorkus to ease bookeping and relmon-ification of generator relvals
-  the labelling will become effective once the content of the GEN relvals will be back-ported to 71 (@bendavid @inugent: gen fragment missing)