Wondering if there's a way to import/specify a WMM file, and separately, if the WMM impacts the routing algorithm? 
I ask because as we analyse reanalysis data for previous races, and want to find the routes that would have resulted at that time, I want to make sure using a newer WMM won't have too much impact on the results. 

The WMM could have big differences, especially near the poles, but if it isn't used by the routing algorithm then it obviously doesn't matter.