Check your ticket conditions for the change fees applicable, and the ‘go-show’ allowances.

Unfortunately, I am not sure how a MH flight on WY ticket stock will be treated otherwise… MH has shifted to a different structure for their tickets: each FBC has 3 strata, which define the change fees, not the FBC itself, one selects between Lite, Basic & Flex/Shuttle at booking time. (I believe all 3 apply to MH D as well on MH ticket stock.)