When making changes to a hard link, does it affect the associated source file?

A hard link is an additional name for the same file in the filesystem. When the content of the file is changed through any hard link, the changes are reflected in all other links because they point to the same inode (physical object on disk).

That is, if you modify the file via a hard link, you are actually changing the original file, and all other hard links will show these changes.