I am not at all familiar with the ofxCvPiCam package, and so I’m afraid that I won’t be able to be very helpful. In general, if it works with the camera module, it will work equivalently using PiCapture (the Raspberry Pi can’t tell the difference).
A couple of ideas:
— generally, the “mode” would be established at the time the object is created. I don’t think that MMAL can deal with changing the resolution/camera mode after it is set during initialization. The “setup” method in the ofxCvPiCam example code (cam.setup) has parameters for width and height, and might be something to try
— you might look at the source code for raspivid and see how it handles initialization of the camera.
Please post the solution if you find it – there may be others that are interested in using this package. If you are stuck, I may be able to look at it in a week or so and try to help figure it out.