Here is one method that assumes that you have already been using NuMorse for a while so that the program has been able to gather some statistics on your performance.
1) Set up NuMorse according to the instructions in Play Random letters, numbers or punctuation.
2) Press Alt-T then p, or the program settings toolbar button:
3) Select the Filter tab to open the code filter .
4) Click the Stats button
5) You should see certain characters highlighted in red in the filter window.
6) Click the Start button in the main program window to play code.
Note: After changing filter settings don't forget to change them back when you want to copy normal code.