I have just added a cool feature to Romancing Saga 3: when the inventory is full, you CAN'T change your equipped weapon since the original algorith is:
1) Check if the weapon is in the inventory
2) If so, add 1 to the amount of that item; if not, insert the item into the inventory
3) Pull out the weapon of the character equipment
4) Last step, the user selects the new weapon to equip
If your inventory is full, you can't complete setp 2, so the error sound play and you can't do anything else. But you really could change your weapon if you "swap" them: you pull out one weapon from equipement and pull out another one from inventory, so the first one is inserted in the inventory and the second one inserted in the equipment.
Well, that's the improvement I just added to the game: now if your inventory is full, you still can equip one weapon (or armor or whatever) without releasing an inventory slot previously.