So, aspecting a body's aether to a particular element can happen, most commonly with tempered folk. Even the ones that aren't mutated are aspected towards their primal's elements, as that's part of what tempering is.

This is, of course normally accompanied aspecting of their mind (memory) and soul aether, and the combination of these is what leads to them being enthralled by their makeshift deity. If the memories aren't present, the tempering is not complete. This can be seen with Gaia, who, presumably, is still aspected towards Darkness as she has control over it by her own admission yet does not seem to worship Zodiark. Of course Zodiark's tempered might be different as we do not know the exact changes between the original Deity concept and the corrupted summoning rituals perpetuated by the Ascians, but I digress.

If in your roleplaying adventures, you want to have your character's body's aether be aspected towards a particular element, as long as it's not too aspected, the character should still mostly function as a normal person. Even if this weren't the case (someone can correct me on this), in the end roleplaying is about self expression and does not need to stick too close to canon. However if you wish to have your character struggle with the imbalance of their body (small mutations that they keep hidden or something like that) or fear loosing control, well, overaspecting could be a compelling way to bring drama into the proceedings.

In the end it's all about having fun and telling stories to and with each other, so don't be afraid to cut loose, even if things aren't exactly 1:1 to lore.