I think it is a wise choice to change your trains to give a more comfortable connection.

On the other hand, that is a LONG day on trains. If at all possible, I'd suggest stealing a day from your itinerary somewhere to build in an overnight stop somewhere along the way. I have been on almost every mile of your proposed route but never all in one day. I get cramps in my legs just thinking about it. If you are traveling with older folks, they would undoubtedly appreciate a break to stretch out along the way. I know i would.