This mod allows you to remove souls from soul gems. Right clicking on any soul gem in your inventory opens a container. Drop the soul gems you want to empty in there, close your inventory and wait a moment. You will recieve empty soul gems.
This works with pre-filled gems as well, so if you find that grand soul gem with a petty soul inside, just get rid of that junk!
On the other hand, you have an empty soul gem and catch a grand soul, and the price doesn't change? No more! Now you can convert the soul gems you just filled to the pre-filled ones found in the Construction Set.
An optional file is available, meant to be merged into the bashed patch (though it can be used without the bashed patch, if you have nothing that changes soul gem graphics). It will change the prices of the pre-filled soul gems to be price of empty gem + price of soul. This will make buying pre-filled ones less exploitable (a grand soul gem with petty soul would cost 40 before, now 240), but also give guaranteed profit by selling filled gems vs empty gems (empty petty gem sells for 10, filled petty gem sells for 50).
This one took way too long.
I had to completely rewrite it how many times, because Oblivion doesn't like edits to soul gems. In the end, I am happy with how it turned out, it requires some more clicks than the first version, but allows full control, which is even better.