Happen to know of a way I could modify it myself?
The fact that you ask that question means the answer is no

If you know how to code and compile it would be simple to alter the source code.
Otherwise, someone would have to compile a special version for you or add Imperial units option to CHDK.
A special version would need updating every time CHDK is updated.
On a practical level, for non-close-up shooting, the DOF of small-sensor P&S cameras is so great that you do not have to concern yourself with it.
For close-ups, if the DOF is not sufficient, what can you do anyway ?
A smaller aperture (if your camera has a physical diaphragm) is not a good idea because of reduction in sharpness.
Remember, f8 on these cameras is typically equivalent to f32/f40 on a 35mm camera !
For close-ups with SDM, I focus on the nearest subject (in continuous shooting mode) and press the shutter button.
It adjusts focus with increasingly larger steps until infinity is reached.
David