Sustained loads are not the problem so far as compressor nozzles and similar are concerned. Normal practice is to ensure these loads are zero by careful alignment and spring support balancing. The mating flange will usually be required to be practically perfectly aligned when the bolts are removed.

Consequently, loads to be compared with NEMA / API617 tec. should be thermal and displacement in nature.

Thus, I would say that use of Graylocs will not help nozzle loads. However, a length of smaller size pipe local to the nozzle, rather than a reducer actually on the nozzle should have a significantly beneficial effect. If you can get it past the process engineer.