Yes, if the first URL return a 404 error. Normally, if the file exists, the web server send the file to browser without call Joomla. If the file returns an error, you can tell the web server to pass to Joomla (and ReDJ) any error, just adding this line at the end of .htaccess file:
Now you can create a rule to redirect the request using ReDJ:
From URL: ^/downloads/obs40/obs40.exe$
To URL: http://{siteurl}/downloads/peeradmin/40/peeradmin40.exe
Request only: true (must be checked)
Redirection type: 301
Best Regards,
Luigi