Hi DDeGamnes,
I owned also an SX230 and I was able to increase the focal length of it with CHDK from 28 mm to round about 24 mm by using the DNG mode: Note that the SX230 naturally is not able to write RAW but by utilizing chdk it is able to write DNG.
There is a lense profile for Lightroom for this SX230-DNG which removes the distortion and the black areas in the corners (cropping). By doing this the result was an image with 24 mm of focal length. This is a huge benefit over the built in 28 mm.