Chatting with an area mechanic, a shop will often chop the seatpost right before sale, so you mustn't have to bother with this far too much however, if you are doing have to, Will not stress as it can be done! Only for reference this was for a size 51cm https://cervelotimetrialbike49494.arwebo.com/49693952/stationary-bicycle-things-to-know-before-you-buy