I believe that the game code could easily handle this already as it appears there are mechanics in place already that at least check the glamour to ensure it can be equipped by said class. If we treat the glamours similar to materia, in terms of a stored piece of data on the item, then it seems like it would be feasible to utilize the existing system of checking the glamour prior to applying graphical appearance based on job. The logic would be for the system to check the job of the player, then based on the job select the appropriate glamour slot, then apply the graphical appearance. In this case whatever job you are when applying the glamour is how the system will know what slot, and how, to "affix" the glamour slot. e.x. As a PLD I glamour the Weathered Noct Lorica to appear as Valor Surcoat. Because I am currently a PLD when applying the glamour the system saves appearance Valor Surcoat in slot 1 as condition "Must be GLD/PLD for appearance to take form".