I believe that several carriers (for sure United and I think others) will let you change for free on a Max. The issue for you is going to be the impact to your

I believe that several carriers (for sure United and I think others) will let you change for free on a Max. The issue for you is going to be the impact to your time, which is likely more valuable than the change fee to begin with. On the standard consultant route of Monday morning/Thursday afternoon there are many times not alternative flights for hours (or possibly days) later -- especially if a Max gets "subbed in" at the last minute and you cannot plan ahead. The change fee will be inconsequential compared to you not showing up on a client site for a day or at all.