A 2x barlow is 2x only at the spacing it is designed for. Decreasing the spacing reduces the power by the amount you reduced the spacing. Cut it in half and its 1.5x. Double it and its 4x. Put it in the eyepiece and it is just about 1x, hardly does a thing for you. If the eyepiece focuses beyond the barlow it will reduce the power to less than 1x and likely not even focus. Never tried it. I never had a barlow that would screw into an eyepiece.

Barlows alone can be used to project an image onto film or a CCD. Often with better results than using an eyepiece. I never tried both in all my years of film work! Altering the distance the eyepiece or barlow projects to the film gave me all the image scale variation I needed. One eyepiece, a 12mm symmetrical so I could use it upside down as well as right side up to change projection distance was all I used for higher powers. For lower I used barlow projection alone. Both work like a slide projector. Think of the barlow or eyepiec as the projector and the film as the screen. Put the screen farther back and the image is bigger but dimmer. Enlarge it much at all and you will need a drive to track the earth's rotation. You might get away with barlow projection this way but certainly not eyepiece projection. The image scale will be too great for the available light, especially with film.

Rick