Fiddling with the damage or penetration definitely shows up ingame, so at least I now know that my changes are read by the game.
Too bad that beam-width doesn't seem to do anything at all either, like the three colour lines.
And I finally had a breakthrough for my original attempt. Since this had be stumped for near enough an hour, I might as well share to safe other people the headache: If you want to use any effect on a unit, that wasn't made for that unit specifically (like for exmaple using the psi_carrier's beams on the psi_battleship) you have to add this effect to the .unit_skin file of the unit, or you'll get a missing definition error.
Thanks for the help.