It can be done. The same can be done with the S&W M&P 40. The M&P 40 mags feed 40 S&W and 357 Sig. Soooo... Just order a 357 Sig barrel from any of the big guys, Brownell's, Midway, etc. Pop it in, and use the exact same mags... and it feed and fire 357. It can also fire 9mm. Order a barrel, new mag(s), and away you go. So you can have basically one frame that shoots 3 calibers by switching out barrels and mags. Can it be done the other way? 9mm to 357 Sig or to 40? Don't know. Will I try it? If I had the money? Sure, why not! I'd also need a S&W M&P 9 to start off with... Heh heh heh. Anyone interested in fianancing such an endeavor?
Can it be done with Bersa Products? I think so. But I'd go from 40 to 9 and not 9 to 40. That's just me. I have a UC9 non PRO. and I like it just fine.
Keep your Powder dry...