You could pause then enter the depth you are wanting into the DRO, eg if your code says z-1 but its only cutting z-0.8 you could enter -0.8 into the Z DRO press the enter key and resume. However you would have to be carefull as the prep move would likely call for a rapid into your work. You would really need to pause, stop then go back to a line before the Z has gone into the workpiece and change the DRO to suit then do a Run From Here.
I think though you need to get your problem sorted by finding out why it is not cutting at the depth requested by the code. A few things that I can think of are
You dont have the steps per unit correct for the Z
You didnt set your zero Z Height correctly
You have an offset in the tooltable set incorrectly
Your cutter is moving up into your collet
Hood