Yes, it would be legal. You should be very clear with purchasers about the value-add so that there's no trademark issue, where people think they're buying a gen

Yes, it would be legal. You should be very clear with purchasers about the value-add so that there's no trademark issue, where people think they're buying a generic "Foo Brand Router" but they're actually getting Foo hardware with Bar firmware that acts totally different than standard Foo hardware.