[REQUEST]Content Add-On and Mission Select

Okay, after completion, I wish my AC project to have the ability to utilize add-ons, such as new weapons, AC parts, missions, etc. My question is, how would I go about allowing the player to install these add-ons without re-installing an updated version of the full game?

Also, as is the tradition in all Armored Core game, I would like to know how to make a mission select screen, preferably through eventing, but if not, then sripts are fine. What I am thinking of is a scrollable screen displaying possible missions to select and sortie, after completion/failure of the mission, the mission is replaced with another, such as Armored Core 4 works.