does this mean it should be relatively easy to switch out the axle and use it as a rear with a bolt-on fixed cog?
Design of the substitute axle should be trivial, but a front disc wheel dished correctly for the front brake gives a narrow (~41.5mm) chainline when you bolt a cog on it, whereas your SS freewheel hub will be at least 45mm, and can be pushed out to 49mm to match the chainline of a bolt on cog on the other side of a rear hub
Design of the substitute axle should be trivial, but a front disc wheel dished correctly for the front brake gives a narrow (~41.5mm) chainline when you bolt a cog on it, whereas your SS freewheel hub will be at least 45mm, and can be pushed out to 49mm to match the chainline of a bolt on cog on the other side of a rear hub