The names are hard-coded in both the AbelCam app and the java player that comes with AbelCam. It sounds like you are using something else ("other appl. on the PC") as the player, right? If that is the case...
Use the AbelCam Proxy (Configuration -> Proxy) to "alias" the mjpg stream(s).
Name: TEST (or anything you want)
Address: video.mjpg
Remote URL: http://localhost:8080/current0.mjpg
Now "current0.mjpg" will be served when client requests "video.mjpg".
Notes: Proxy feature is
not available until you have turned on "I am an AbelCam Expert" in Configuration -> Options! The Address can be whatever you want. You can configure multiple proxy entries for current0.mjpg, current1.mjpg, and so on, as long as each one has a unique Name, Address and Remote URL. In the Remote URL, the "http://" part is mandatory - if you leave it out nothing will work. The port number I used (8080) is the default - use whatever port you have AbelCam webserver to run on.
See also:
Proxy online help