Yes, unless you can prove to RCI they are unresponsive to the point they take away the booking from them. The TA lying to you that they are limited in the number of reprices is not a reason RCI will take away a booking.
I don't believe that to be true - every time you reprice, it further eats into their commission so of course they want to avoid that (and they'll make up stories to dissuade you from it).
No.
If the booking allows it, there's no limit how many times you can reprice. There are several reasons why you can't reprice, like inside final payment, sailing booked in a market which doesn't allow it, booking for new booking only, etc.
GGG = Going Going Gone.
It used to come out on Thursdays before COVID - after its return it moved days a few times before settling on Monday effective Tue-Wed.
That may vary a bit depending on the ship.
Check in can be done online or the app.
You select an arrival/check in time, not boarding time.
You can book MTD times before sailing or on board.
You don't have a choice - they are added automatically on the ship and you have to take action to remove them.
Biker, who wonders how many would remove them if the option was added to the app.