The OnePass I would think is stored on the box itself. PRobably just takes a few moments to set the new box up for that. I'd recommend removing the info from the box you are getting removed before they arrive though.
They have to come and set it up because it involves setting it up for your account, line-up and also connecting any minis to look at this box instead of the old one - that is if you have any minis. There are probably other reasons too.
Cogeco - Mix 40, Timeshifting, TiVo T6 DVR & 2 Minis, UltraFibre 360; Rogers - LG G7ThinQ; Koodo - Wireless Home Phone