Can you please clarify your requirement - are you trying to filter the offer's data for run time usage ? like evaluating the offer based on the custom attribute that is set or you want to change the design time UI ? if so which design time UI - is it your own or you are trying to take over the offer rule form ?
It would also be better if you can explain the business requirement better - so that we can suggest the right recommendation. May-be there is OOTB features which is already built to serve your purpose.