Adding filters to your camera without removing the original will just add weight to your gimble theres no point.Is it you have a problem removing the original.
There is a kit of thin plastic films you can place on the inside of the lens. This keeps the original lens but you will need to unscrew it and replace or remove the film as necessary.
The more you put pieces of plastic or glass in front of a lens the more you degrade the quality : this is true for every lens, even premium ones.
The Phantom picture quality being what it is (bad), it is better to avoid adding a filter over another one.
I tried them and they were horrible, flimsy, and impossible to install or remove, with out getting fingerprints.
A little thicker than saran wrap, but not much, if you are installing them do so in a wind free area, or they will blow away.
They couldn't cost more than .99 cents to manufacture. but cost $28.95 or $34.95.
I have DJI filters as well as Polar Pro filters and they all work great.
Unscrewing is a bit difficult, but if you hold the lens with 3 fingers equally spaced around the lens cover and twist without squeezing too tight it comes off just fine.Be careful whe removing the lens as to not lose the rubber o-ring.