I included an alternate laser sprite for this very purpose, it's a little fiddly to get working and still covers the screen with a color, but translucent red is at least less eye-searing than white.
You'll want to open the PK3 with Slade, open the Players file in Actors. Hit ctrl + f, type XBEM B in the first box and XBEM A in the second and hit replace all. Then head down to "laserbeamparticle2" and replace those two specific XBEM As with XBEM B. Doing it this way will be a lot quicker than manually replacing all 37 frames of the offending effect lol.