You can unpack it (rename to .zip and extract) for educational purposes. However, modifying and repacking will break the digital signature, and Chrome will reject it.
This .crx file is the "glue" between your standalone IDM software and your web browser. Its primary job is to and redirect them to IDM for faster, multi-threaded downloading. Without this specific extension properly installed, IDM often fails to "see" downloads starting in Chrome. Performance and Features idmgcext.crx
Once installed, IDM works automatically: You can unpack it (rename to