Question: How hard would it be to turn a 2-8-2 into a 4-6-2
For a mod like CN S1b to CP G2, you would need to own the mesh and learn Blender to alter the features. To just switch out wheels, you would need to dive into the Trainz wiki and learn how to manipulate the bogie tag in the config file. The results will depend on the level of plausibility you are willing to accept.
Midnight Coal