Good idea... I just worry with infection being so close to the brain there...
As long as he doesn't escalate to biting, it's not a big deal... if it becomes an issue, just gently pin him down with your hand until he stops struggling any time he gets aggressive...
Calls imprint much easier than other ducks, so they tend to see themselves as part duck/part human... that's why they will do it to their humans sometimes... also, being 2 males and no girls might be another factor... once you have girls for them, that may stop... or it might escalate... just use your judgment... luckily since they're so small and round they're not as difficult as a large breed duck getting aggressive...