Hm, maybe they changed that in a more recent version. Last time I tried (one year ago or so), the program simply refused to start after the end of the trial period. There was also absolutely no documentation available at this point how to get the non-Pro version and the Pro version did definitely NOT change in a non-Pro after the trial.
Then again, there's nothing in this GUI I want to use anyway. For the 33120A, I used the GUI only to upload the arbitrary waveforms, but on the 33521A there's no need for this either.