https://forum.square-enix.com/ffxi/t...l=1#post545505
Patch notes for FFXI from March 26, 2015, listing the revamp of /lockstyle and the addition of the /lockstyleset command, allowing players to glamour any piece of gear as long as they can equip it on at least one job.
This was not an exploit but an intended feature introduced by the devs. The only thing that doesn't make this "free-form" is the requirement that the player has to be at least able to equip any piece of gear on one job.
It's also worth noting that the final expansion, Rhapsodies of Vana'diel, had not released at this point and that it would've been very difficult for FFXI's dev staff to have been reduced to a bare minimum at that point.