Hello,
  I have a 2018 500ho that has 249 miles on it.  I'm getting ready to do the fluid changes but was wondering if I should take it to the dealer and have them check the valves?  I read that this should be or needs to be done on these machines?  I am also going to re-clock the secondary to C1 because I put 26" tires on the machine and it seems to need alittle more get up and go.   

you can chech the valves yourself as well. I recomed to check them somethimes especially the firts breake in check and adjusting if needed.

You don't need to clock the secondary for 26 (depends on weight and true size) but it should give the machine a bit more "power" and compensate for the tires.

[2015 Z Force 800 53/Trail EPS]

Good idea to at least check them. No reason you can't do that yourself. And where it may not be required, C1 is a good setting for all 5 and 600s with anything from stock to 27" tires.