I assume you are referring to CA Performance Management 2.x?
There is a REST API, but only allows you to update 1 interface at a time...
* Speed In/Out Override Rest:
PUT http://DAHOST:8581/rest/ports/PORTID
Header: Content-Type: application/xml
Body To Set (replace SPEED with the override values, and if you wish to just override Out, just remove the SpeedInOverride line):
<Port version="1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<SpeedInOverride>SPEED</SpeedInOverride>
<SpeedOutOverride>SPEED</SpeedOutOverride>
</Port>
Body To Clear (if you wish to just clear Out, just remove SpeedInOverride line):
<Port version="1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<SpeedInOverride xsi:nil="true"></SpeedInOverride>
<SpeedOutOverride xsi:nil="true"></SpeedOutOverride>
</Port>