Cancellation loop hole

[Ben-And-Robyn0]

We have a strict cancellation policy.  Recently we had a guest wanting to amend their booking.  ( number of people ) Which we happily did.  However by agreeing to an amended booking it allowed the guests to cancel their booking within 24hours with full refund. 
once bitten…. Now we have someone wanting to amend number of days staying over the holiday period.  I would happily shirted their stay but my fear is they are using the loop hole to cancel their booking

i would like airbnb do something about this loop hole.  So the cancellation period starts from the time of the initial booking.  
what do others think ? 
thank you 

Robyn 

[Emiel1]

@Ben-And-Robyn0 

Regarding the first mentioned amend (number of guests):

Was that change request created/sent by the guests (and you accepted it) OR was it created/sent by you (the host) and the guest accepted it ?