The quick answer is yes– it’s your radio, and your counter, so you can do whatever you want with them. You won’t even void the warranty, unless there is a problem caused by the “modification.” But in fairness, I have to say it is not a real good idea. Let me explain why we don’t offer a digital display as an option, and invite you to reconsider.
The primary reason is technical— frequency counters are based on microprocessors, and microprocessors operate at radio frequencies. Therefore frequency counters generate RF noise which must be prevented from getting into the receiver. The only “authorized” microprocessor in an OHR radio is the optional electronic keyer– even there we usually recommend building the keyer as an external accessory.
The secondary reason is economic— a large part of what you are paying for in an OHR DD-1 is convenience and flexibility– features that are essentially “wasted” if the DD-1 is built into a radio and can’t be used with anything else.