It is my plan to distinguish from the other. Perhaps in user control panel there will be an option for them to switching it, but this could be hard to manage and bring a lot more headache especially when need to deal with a difference between each server which could brake the current site.
So is there any easy way/less headache to deal with this situation?
We have users on a regular basis move between platforms and packages. We've found that when having users upgrade between software levels, they're more inclined to "upgrade a hosting package" - even if it's the same price. This way, we can make sure that the client definitely knows what they're wanting to upgrade to (and why) and then the order is placed in PENDING until one of our admins perform the move task and the package is set to ACTIVE.
For us, we change the IP number as often times, they're moving from a US server to a UK server or whatnot - and upgrading from a general shared account to an ecommerce account requires a dedicated IP number, so that's a move on our end too.