String replacements are not performed by default. If you want them to be executed automatically, go to "Settings/Configure Kid3.../Files" and make sure that "Format while editing" is checked. If this checkbox is not checked, you can perform the string replacements using the menu "Tools/Apply Filename Format".
The same options exist for tags, its "Format while editing" checkbox can be found in "Settings/Configure Kid3.../Tags/Tag 1 and Tag 2" and the manual menu function is "Tools/Apply Tag Format".
