Reversal of natural gas pipeline flow has occurred in the past, see the link. I recall projects and designing valves suitable for bi-directional gas flow (and have a patent on bi-directional low noise valves). While much more common on storage facilities for injection and withdrawal, some major pipelines have had this feature built it to account for seasonal variation. With the potential for addition of LNG import stations and possible hydrogen injection, seeing bidirectional flow can occur. This impacts more than valves, as compressor stations then need to be reversed and switchable through piping modifications.