First off, is it recommended to tow with and D-rated tire?

Maybe 10-12k pounds, sometimes more.

I have a 28’ camper, 8k dry and around 10-11k wet/loaded.

I’d also sometimes carry alfalfa bales on a 20’goose neck.

Since many people regear with 35x12.5 tires, will 35x10.5 require regearing?

Kenda Klever RT 35x10.5R17 would be 3197@65psi.