Hi cats_pajama,
I based this tag change on the guidline found in the wiki page of highway tags in Africa (https://wiki.openstreetmap.org/wiki/Highway_Tag_Africa). The wiki state that highway=trunk should be used for “The most important roads in a country’s system that aren’t motorways. (Need not necessarily be a divided highway.) Note that such roads can be unpaved.”

Given that in these countries National Roads (RN, NR or N, depending on country) are the most important roads, then trunk should be the most apropriated tag for these. 

Do you think another classficiation is justified for these national roads ?

All the best,
AlkalIn