[botmeister]

In the mEAn install folder you can edit sounds.cfg and change what the bots say.

Look for this:

!botyell
misc/killingspree.wav
misc/ultrakill.wav
misc/multikill.wav

All you have to do is change the sound files listed under the sound command "!botyell"

You can delete, replace or add files. See the header comment in sounds.cfg for more details.