Glamours should always be applied to the
slot, not the gear item itself, and on a job-by-job (or class, apart from SCH/SMN) basis.
Each job should have, say, 3 images available to each of its slots, with 3 glamour "sets" available for quick swapping/matching. Glamour prisms are consumed to add an item to the bank of 3 images per gear slot per job, or, if those slots are already full, to replace another image.
By default, any other images saved on any other job that your current job meets the level and class or job requirements for will be shown in your image slots. (Swap from a glamoured level 40 Warrior to a newly gained Paladin and it's no problem; you'd immediately see the applicable (even if incomplete) sets from you warrior in addition to your native/unglamoured set/look.)
Moreover whenever you spirit-bind an item, you have the option via a right-click (notification once out of combat following the spirit-bind) to save its image to your glamour bank (replacing another image if the bank is full).