When building a plug-in on the plug-in management page, it will not be selected if it is not signed. At this point, you will generate a crx plug-in file and a pem key file. When you are developing, you can ensure that the id of the plug-in you build is the same every time.

Also, uploading to Google Plug-in Center is not uploading crx files, but uploading zip files packaged in the plug-in directory.