The way I read it, when the upgrade to Nexus is completed all your secondary stats will be bumped to i115 levels. If however, you wish to change them, you can procure a new Sphere Scroll and pull the stats off the Nexus weapon to redo. When you do this, the stats will be returned to the level they were at when you melded them into the Novus weapon.

So if you were to do this, you'll also need to get the extra Alexandrite and Materia needed to finish the number of melds up to i115 levels. Also, given that we can currently edit and remove melds from the Scroll before it's added, I'd assume when the melds are pulled off the Nexus we'll be able to do the same thing. For people that do that, they will need to get the extra Alexandrite/Materia for those stats they are changing as well as the Alexandrite/Materia needed to add the stats up to i115.