There is a tutorial on hacking the core files included right with the release! (called hacks.txt)
Apart from that, the core-file hacking is absolutely safe and can be done with one mouse-click from the backend.
As I've said on other occasions here - we are currently working on the finishing steps to release RC2, which will be our most stable release to date and clean up the stuff that others have reported with RC1.
From the reports that we got so far, our CB Integration was a full success and is working for everybody. (At least thats what our customers report.) We have also included support for CBE in the upcoming RC2 and cleaned some minor issues with the general CB integration.
I will open a new thread when the release is ready!