A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,413
If a schedule changes puts your itinerary below MCT, you will be changed for free, even if low award must be created for you, although you might not have 100% free choice of new flights--for example, if two flights both give new legal connections and one is very full, you might not be allowed to pick it.
Without a significant schedule change or one the violates MCT, to change you would pay $150 per ticket plus more miles if the new flights aren't available in low.
I have answered for passengers with no status and where the miles did not come from an account with status. High tier elites do not pay change fees and are more likely to have reasonable requests regarding tight connections granted.