This mod should be lower in the list of mods than the Bugfix mod as both mods change the same functions. The Bugfix mod simply fixes some typos, so it is fine to override those changes. This mod does not need to use tags like AddTo or Remove from as without tags the mod system defaults to adding new or replacing existing definitions. The Bugfix mod also uses untagged changes. The mod that is lower in the list is applied later and for definition replacements this means that the later change overrides the earlier change.
This mod (and the mod system itself) is simply the automated version of copy-pasting the text over the relevant sections of the original game files. If you wanted to do it manually, then the results should be essentially the same. Though it may be worth investigating why it is not working for you. If I were to guess why it doesn't work, then I would say that since the download was not packaged as a archived folder you may not have setup the mod correctly as all of the pieces are essentially necessary. The site offers the option to download all the files as a single zip, which can be extracted into a folder of the same name. It should look something like this:
- mods
- Mana for Baby
- info.txt
- scripts
- Mansion.gd
- Mana for Baby
If it still does not work for you, then I recommend checking that there are not errors reported by the mod system. If you have 64-bit Windows, there is also the option to get the Debug mod, though the mod system generally reports most errors without needing the additional output window.