Given how I got to Electronics (I went from Hardlines/Cashier to pretty much all Electronics after one of the main Electronics guys left our store), I think that's a pretty big jump given that you probably haven't been trained in zoning aisles and all the other main salesfloor stuff. There is a little more to Electronics compared to doing regular salesfloor like tracking attachments to items sold and keeping a closer eye on guests than you normally would since Electronics is usually the place where a good chunk of thefts take place, but it's really not a lot and will become second nature to you after a few shifts. Plus, unless it's Christmas/Holiday time, you generally don't have to worry about working in the busiest/worst part of the store.
In terms of calling it a 'promotion', I wouldn't really call it that unless your store is short of TMs who can do full shifts in Electronics (much like my store). If that's the case, then you'll probably get a lot more hours compared to your co-workers who are nothing but cashiers and/or some other position where there might be more people working that area/department than they need in a given day.