No. With the override function you can scale the velocity only between 0 % and 150 %. Negative values are not valid. If you want to reverse the direction, you will need to load a negative velocity value and send the Start Motion command. The result will be the same as scaling the velocity to a negative value.
The only disadvantage of this method is the fact, that you have to send two sequential commands instead of only one, which will result in a slightly longer execution time of the code.
I hope this helps,
Jochen Klier
National Instruments