Hi Jefferson,
If you was changing the edit widget according to your custom application, you would need to make changes to the .xml file present at the below location: C:\Inetpub\wwwroot\flexviewer\widgets\Edit\EditWidget.xml
You don't need to make any changes to the .swf files present. If you would be working with the Source code in Flash builder and creating any custom widget in an mxml file, once you builds that mxml file it would generate a .swf file
Hope this answer your question.