Can you change the performance dates for your show after having sent in the completed contract?

Before sending in my completed contract, I asked everyone in the show if they were available during the performance days, and they all said yes. Unfortunately, quite a few of our performers forgot a trip they had already paid $500 each for that was non-refundable. 

I really don't want to recast the play, since we just barely had enough auditions to put it on, and I'm not sure we'd be able to fill all the roles if we tried to. 

Is there any chance that MTI would let us change the performance dates by a week?

In case this changes the answer, we're putting on 2 performances of Into The Woods Jr. in May, 2019. 

Thanks, 

Kye