1. Keep an original copy
Make a backup before opening a configuration. The .cfg extension is shared by many applications: one may use INI sections, another JSON, another a command language. Check the application documentation instead of assuming the extension tells you the syntax.
2. Open and inspect
Choose a local text file or paste its contents into the editor. BOMs identify UTF-8 and UTF-16. When UTF-8 decoding fails, the tool suggests Windows-1252. Check accented characters and choose a source encoding explicitly if needed; encoding detection without a BOM is uncertain.
3. Make a controlled change
Select the syntax, find the key using literal search and change only the intended value. Search replacement treats the replacement as literal text. Use the validator to catch the problems it supports, then compare the modified text with the original. Neither step verifies the application’s full configuration semantics.
4. Download and test
Choose the filename, encoding, BOM option and line endings your application expects. Download a new copy. Test it in the target application and keep the backup until the application starts and behaves correctly. Closing this tab discards its contents.