Just be certain that you are not running other components from the PS300 that could be harmed by the different frequency. In this regard, when the Power Plants were introduced, some manufacturers claimed that use of PS Audio multiwaves with their equipment would void the warranty (ARC may have been one, I seem to recall). Not sure how this could be proven - the change affects the rate at which caps in a component are replenished - but you should be aware of the issue.
PS - I have experimented with changing speeds on my VPI motor by use of my PS300 and the other posters are certainly correct - it works - but given the above consideration and the other components also run from my PS300, I just move the belt for 45 rpm play (I only have a small handful of 45's).