A better solution is as follows:
Modify the board file (as you probably did)
Create a project with your "TEST BOARD".
Go into the "TEST BOARD" project delete the core folder (you first have to right click the arduino folder -> resource configurations->exclude form build because CDT .... -see my fact for more details-)
and then use the import wizard to import the "test" folder under /hardware/arduino/cores/ in your "TEST BOARD" project.
This is exactly the same as the fix will do in the future.
Yes.. good solution. Thanks.