this sounds weird... mount a cdrom to see a video??
i am not sure what you are trying to do but just as further reference:
1. you don't need to mount a dvdrom to be able to watch it
2. in slackware if you installed from the source with the classical
./configure && make && make install
there is not automatic way to remove the package.
Seems it's as simple as:
but perhaps a slack user could interject here....
removepkg mplayer && installpkg mplayer
this only works if you installed using pkgtool or something equivalent
I also need to point that Mplayer has a great docu. how to edit the config file is included there.