The most challenging and important part of an upgrade is porting code and data modifications from the older version of a system to the new version. When the new version has major design or data structure changes in an area that we have customized, it is quite possible that our modification structure will have to be redesigned and, perhaps, even be recoded from scratch.
On the other hand, many times, the changes in the new product version of Business Central don't affect much existing code, at least in terms of the base logic. If our modifications are done properly, it's often not very difficult to port custom code from the older version into the new version. By applying what some refer to as low-impact coding techniques, we can make the upgrade job easier and, thereby, less costly.