I have been intentionally non specific as to IAS/CAS, as I'm not trying to describe a specific speed. Rather, my intention was to suggest a slower speed range, below which flying is not being suggested for the purpose of a newer pilot getting to know the plane, with full rudder application.
I am required to carefully plan and plot speeds, corrections and IAS/CAS for testing, and record what I have observed. However, I don't suggest doing so adds value in this situation. It's just an attempt to give a new pilot some confidence that yes, those controls are intended to be used to the limit in some phases of flight, and here's such a phase...
I agree that full rudder deflection puts you way out of co-ordinated flight, and surely introduces pitot errors. However, if you enter uncoordinated flight at 1.4Vs, and maintain that airspeed or faster, I propose that you will maintain a safe flying margin - particularly in a Warrior.
The standard calls for 1.2Vs to 1.3Vs for this testing, so I would thing the newer pilot is safe at 1.4, even if IAS to CAS is overlooked. This should also cover yaw induced pitot position errors, at least to the point of being safe.
For a King Air B200 project, I was required to verify yaw stability and control at full rudder deflection at 1.2Vs1 CAS. That aircraft has a special condition which describes the possibility of yaw angles as great as 38 degrees. I did not have an accurate means of measureing the yaw angle I achieved, and I don't think I got that high, but it was sure going sideways. A very controllable aircraft, and there did not seem to be position errors which made me uneasy maintaining safe, controlled flight in this configuration. The boom out the back I was testing was sure wiggling though!
My prime thought is that some pilots have not come to relax with the reality that they have a lot more control than they think, if they simply put the intention and muscle into using it. Pilots should not spend their entire flying time, just going straight and level with their chums, or wife and kiddies. They should plan a flight under appropriate conditions, within a safe range, and the aircraft limitations, and see what the plane can actually do. Many would be surprised! (and they'll be safer afterward)