As stated above, racial abilities are implemented in the relevant code, which for fairies is the end of day in Mansion.gd.
Generally, I have recommended against people playing using the debug mod because if an error occurs then the may game will continue playing and can be saved, which can cause permanent data corruption. However, recent investigations have revealed that some errors can still occur without crashing the game in non-debug mode leading to similar problems. As your changes are quite small and vanilla is very stable, it should not be a problem either way. Though if you do, I would recommend leaving the terminal somewhere slightly visible so that you can spot error messages before saving.
As a side note, there is a Bugfix mod that fixes many of the remaining errors, though applying it will erase your changes (see above) and version 6 was recently released so it's still possible that it adds new errors.