As far as break in oil goes, I think a lot of people will tell you a different story, including different Generac tech support guys.. Some will say there's no need to remove the break in oil early, some will say there is no break in period required on the new units.... I personally wouldn't worry about the amount of hours you have before you change the oil the first time. Some dealers change it when installing a cold weather kit (even at 0 hours), others wait 20-50 hours as you mentioned, whether or not they've installed the cold weather kit. These aren't high performance race engines, the results between 20 and 50 or even 100 hours before the first oil change are negligible IMO.
I agree with Brian. Unless I lived where temperatures are EXTREMELY cold, I'd leave the original oil in for at least 20 hours or so, and would change it whenever it was convenient to a full synthetic oil, (or as close to full synthetic as you can get these days.) Whether that is at 20 hours or 100 hours makes little difference.
I changed my diesel to synthetic at 25 hours, mainly to have the synthetic in it before the second winter.