Welcome. Mud and trail usage are very different and as such the loads through the CVT system are also very different. The 2012s and up have a redesigned clutch that in general, can handle average muding and simi-agressive trail riding on tires up to 28"(on more offset wheels as rubbing will happen) as weight each up to about an additional 10-11lbs over stock. The stock tires are about 14.2-15.0 lbs. Over that weight or more dedicated mud usage will require clutch tuning, not replacement. Over 28s will require a lift kit. If it were me I would stay with 27s if my riding was 50/50 mud & trails, 26s if it were 60+% trails and 40% mud...and I would pop for a set of wheels that allowed me to run square and 10" wides all the way around with a 7 or 8" width...say 5+3, 5+2, 4+4, 4+3. With these you may want a set of overfenders. Direction2 makes a great set.
If you will be needed a clutch tune VFJ (VFORCEJOHN) is the authority on all the new and old Kawasaki clutch setups. Contact him as to your needs. He has a web site for contact info.