[@johnjamesjacoby Keymaster 15 years, 5 months ago]

@whitehats – You should never, ever, modify any core files. The WordPress actions/filters system is in place to let you inject code and modify existing values as needed. Anywhere you feel the need to hack the core, there should be another way.

The only times when hacking core files makes sense are specifically when fixing a bug in the software or when creating new features to be inserted into core.