Can you play the army missions after completing story mode?

This is not a legitimate post. This is the equivalent of a fan-fiction for video game missions. There are no Army missions for Franklin to experience after the culmination of the GTA V story mode.

This post was not made via a Rockstar Games PR Representative, there was no major announcement with screenshots or videos as is custom for an expansion of this scale, the user who posted about this is "CaptainIce14" - not (likely) a a Rockstar Games developer, and there has been no follow-up from this three year old post.

The first and only response to this forum post is somebody discrediting CaptainIce14 saying

"ooh its you again with your senseless idea..."

which indicates this user often posts gaming ideas without substance.