I have professionally converted several revolvers from .44 mag or .45Lc to .454 casull HOWEVER to do the job right(only way to do it)I machine a new cylinder from blank to 5 shot,replace barrel,adjust timing and lockup,etc. In NO WAY would I reccomend doing it with factory cylinder/barrel. There's a lot of good reasons to convert calibers such as if the model isn't available in that paticular caliber. For example,I like .454 casull in ruger blackhawk or redhawk-NOT super redhawk as the actions of these 2 are vastly different and double action pull is better in regular redhawk from design standpoint.
At some point in their development nearly all wildcat rounds were done like this; refitting existing frames with correct bore barrels and rechambered cylinders. There is no 10mm revolver available, for example, but a Ruger .357 Blackhawk can be rechambered and rebarrelled to create one.