What you want is in the realm of possibility, however; there may be some limitations to how you do it.
1. Creating an NPC that imbues your weapon with a specific element
2. Attaching a pre-existing specialeffect that can be found in the effect_list.txt
So for instance, you imbue your weapon with holy element, find an appropriate effect that could possibly show that they have holy weapon element enchanted. While it does not show right on the weapon itself, the effect on the character can possibly show you are using holy element.
For this to work, you would need a custom auraset command that allows you use effects as an aura. Everytime you use the NPC to change your element, it would change the aura around you.
This is probably the closest thing you can get to what you are looking for