Rodinal will produce less grain with a lower temperature. But high diluted Rodinal > 40-50 minutes is comming to an end.
When going under 15-16 degrees C the developing time in the higher dilutions will be in theory over 1h. So it won't work anymore. Apart from the problem of the rest of your process, fixing on those low temperatures will be also very slow.
A good optimum temperature for Rodinal is around 18C-20C.