arcachofo:
[Don't worry too much about it, now i have a complete arduino instalation for each core and just change path in preferences-Arduino, so i have it working and looks that this is not very useful for most users.
Given CDT's behavior with changing this stuff I get even more nervous.
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.
Best regards
Jantje