This comes up all the time, those with 1911's in 45 ACP want to convert them to 10mm, 38 Super, 9x19 or 9x23. A whole new top end is required as well as magazines, slide stop and ejector.
The problem comes in with the 45 ACP frame. The frame feed ramp in 45 ACP is cut deeper into the magazine well than those chambered in the smaller diameter calibers, so after conversion you may run into feed reliability problems.