Definitely some "leading" questions here by the OP, especially question #2 about "can the service center swap the battery pack without customer knowledge".
Even contemplating that tesla might want to do that implies that there is some sort of disagreement / argument / lawsuit etc happening, because otherwise there is "less than zero" incentive for any tesla service center to contemplate that.
Tying that into question 3 however, the FSD computer retrofit job normally takes somewhere between 1/2 a day and 2 days of the vehicle being at a service center, and I think I had a tech tell me it was 2-4 hours of actual "touch time" back when I had mine done, depending on whether the firmware flash "took" the first time or they had to re flash, etc. It would not take 14 days, unless they didnt have the part for 12-13 of those days.
So we have a situation where, reading somewhat between the lines, it appears that the OP is being told the FSD computer retrofit on their car is taking 14 days at a tesla service center.
My first inclination would not be to think they were replacing the battery, but it WOULD be to think they damaged the car and are trying to replace "something" on it. Could that "something" be the battery? Sure, I guess. That would actually bother me less than them damaging something else on the car that might need body work or something, actually.
it would be kind of nice to know whats driving the questions though, as no one would just think tesla is replacing a battery pack in their car and trying to hide it "out of the blue".