You can not turn the slice upside down. The trick is to do as they say. Use a brand-new portion of a box cutter blade. I buy the disposable utility knives in the hardware store - the kind where you can snap off a piece of the blade to get a fresh tip. I pay $0.99 and it last for many pizzas. If you are lucky, you can wash it off and dry it well and it won't rust and maybe you can use the same tip /edge for two jobs.
If you turn it over, the topping are going to fall off and at minimum get squooshed. Then when you put the two "top" sides together, it isn't going to work right. I always starts cutting at the crust end.
I also did both shops at the same time on the same call. I wrote the same thing for both call sections, and of course for the pickup. I submitted the same receipt (there was only one, of course) for both. The only tricky part is that I didn't know the individual prices for each pizza, but I just expaloined that. The scheduler told me in advance that one receipt was enough, and it was.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008