PS3 version (PSN promo code) gets activated towards your SEN. When launching the game first time, you are required to link your SEN to your SQEX, and hence the SQEX ID cannot be changed as it is associated to the SEN.

For different SEN ID, the player will need to have its own copy of FFXIV for PS3, SEN ID and SQEX Account. If the game already installed on the PS3, technically just a PSN promo code is needed to be activated on the SEN for that player.