as you just need to add one more field in the interface and filter output accordingly enhancing the BAPI would not be the best option. few things you can consider.
i) copy the BAPI in a Z version, add additional field and just filter the records based on input year on a specific place only (it could be a select query or a FM call). yes, you have to debug the BAPI to get correct place.
ii) develop whole logic in a Z program or function. but this will be little time consuming which is not in above case.
i would rather prefer first option as very often we used to get requirements which is very similar to any existing standard object so instead of developing a new better to copy and make desire changes. this saves lot of time and more importantly it will have same look and feel as well as performance as standard transaction has.
Rgds