I reckon that if you did your initial multi in a Duchess:
Nobody operating a 402 would allow you to do a charter (or a private flight) unless you did some differences training in it and a few hours ICUS under your belt. If they did they should have all of their assets in a trust (and not placed there for 'asset protection') because their insurance certainly won't protect them.
If the intent of Part 61 is to allow operators to come up with their own differences training rather than you having to do an endorsement then some how get 10 hours prior to commanding it this is a good thing right?? Problem is, it will be abused by dickheads and ruined for everyone.