Changing mod on weapons?

Can i change mod on my weapon? For example can i replace vamipirc mod on my sword with zealous hilt?

Try it. From my experience, you will be warned if your action will cause an existing modification to be removed. Then you can either continue (and replace the existing mod) or cancel.

So far I have replaced mods on weapons with no problem. But, there is a chance that you will loose the replaced mod all together. I have replaced mods, and then got the replaced one back in my inventory. You will get a warning about it being removed so make 100% sure it's something you want to do as there may be no going back one it's done.