Reply To: Modifying field values for neighboring cells inside a postprocessor
It is perfectly fine to change values in neighboring cells from inside OpenLB operators. However, you are responsible for ensuring that there either A) are no access conflicts due to (in principle) all cells being processed at the same time or B) the access conflicts do not impact the result (note that this is highly probabilistic). This is a general parallel programming issue that you need to think about in any case.
If a (as I suspect you did in c++) sequential implementation is fine from a performance perspective that you can duplicate this in OpenLB as a simple manual loop over the relevant cells.