Use a text editor to edit the file with your profile name in the "\system\save" 
folder in the game folder. 
The last number (37) in this example line corresponds to your marksmanship score: 

561,15,0,15,3,3,3,0,2,6,15,1,11,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,31,

You can change it to the following for a score of 37 
and be allowed to do advanced marksmanship training: 
561,15,0,15,3,3,3,0,2,6,15,1,11,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,37,

This can be edited again if needed to a higher number (below 40) to get to the 
second level of it.