How much change is allowed after a device has been FCC certified?
Since your device is a intentional radiator, you need to be very conservative.  Common sense may say some changes don't matter, but that's a judgement call the paper pushers get to make and it's very expensive to argue with them.  To be fair, some little seemingly inconsequetial changes can effect emissions in unexpected ways.

To be really safe, test your final product and then ship only that.

Get cracking on prototyping with the low resolution DAC so you know which one you want as soon as possible.