if your problem is to only select a part of the road (to be able to edit its tags/properties), but you cannot because every time the whole road gets selected, then … * you first need to *split the road*. Select the node where it should be split and click the scissors icon in the toolbox. Maybe (I cannot run Potlatch myself) 2 myself and do not remember if Potlatch 2 has this feature) you also can could select the node *and* the road's way to avoid also splitting the crossing roads' ways. Also see: https://wiki.openstreetmap.org/wiki/Potlatch_2/Primer#Advanced_edits and https://help.openstreetmap.org/questions/42398/how-to-delete-a-part-of-road and https://help.openstreetmap.org/tags/split/?sort=mostvoted . * Afterwards you should be able to select each part individually and make your oneway change.

if your problem is to only select a part of the road (to be able to edit its tags/properties), but you cannot because everytime every time the whole road gets selected, then … * you first need to *split the road*. Select the node where it should be split and click the scissors icon in the toolbox. Maybe (I cannot run Potlatch myself) you also can select the node *and* the road's way to avoid also splitting the crossing roads' ways. Also see: https://wiki.openstreetmap.org/wiki/Potlatch_2/Primer#Advanced_edits and https://help.openstreetmap.org/questions/42398/how-to-delete-a-part-of-road and https://help.openstreetmap.org/tags/split/?sort=mostvoted . * Afterwards you should be able to select each part individually and make your oneway change.

if your problem is to only select a part of the road (to be able to edit its tags/properties), but you cannot because everytime the whole road gets selected, then … * you first need to *split the road*. Select the node where it should be split and click the scissors icon in the toolbox. Maybe (I cannot run Potlatch myself) you also can select the node *and* the road's way to avoid also splitting the crossing roads' ways. Also see: https://wiki.openstreetmap.org/wiki/Potlatch_2/Primer#Advanced_edits and https://help.openstreetmap.org/questions/42398/how-to-delete-a-part-of-road and https://help.openstreetmap.org/tags/split/?sort=mostvoted . * Afterwards you should be able to select each part individually and make your oneway change.