you are so .... typical... of the mindset of the small bureaucrat...
1. The blue dress "A" uniform (or for officers, the blue-white dress "A" uniform when appropriate to the season) may be prescribed for parades, ceremonies and formal or semiformal social functions. The blue or blue-white dress "A" uniform, as appropriate, will be prescribed for the following official military/social occasions:
a. Parades, ceremonies, reviews, solemnities, and entertainments when the commander/senior officer present desires to pay special honors to the occasion.
b. Official visits of, or to, United States civil officials, officers of the United States Armed Forces, and officials/officers of foreign governments, according to chapter 12, U.S. Navy Regulations.
c. Receptions given by, or in honor of, officials/officers listed in chapter 12, U.S. Navy Regulations.
d. At daytime formal or semiformal occasions.
Please. Do you think it would be appropriate for this young man to wear his high school graduation cap and gown for his boot camp graduation?
His superiors in the Marines tell him what is appropriate dress as you well know since you quoted the regulation. In the same way his superiors at his high school have regulated appropriate wear for this occassion.