yes it is.
it's not the executable file that's illegal to distribute, it's the GRP file. this contains the art, music, sounds, levels, etc. The shareware version of the GRP is freely distributable. The major difference between the GRP files is the shareware only contains the first three levels of episode one.

I'd like to see several examples of the "majority" of these mods that make use of these edited map files.
I know of a couple that might use heavily edited versions of maps outside of E1L1-E1L3, but most use the first three levels. If the majority are using them, then I've been missing out.

People are going to do what people are going to do. If PikaCommando or someone learns the editor and removes the slimers, I would suggest keeping it to themselves in order to avoid unwanted attention. (3dr no longer "owns" the duke nukem ip)

I was mainly referring to mods for any game in general, most of which contain edited or updated files which overwrite the ones in the main game. As the map files alone won't enable anyone to play a game, or do much of anything really, I'd think they remain perfectly legal to provide. For example, from the OP in the stickied thread for Deus Ex mods:

then you'd think wrong
but the chance of someone coming after you is mostly likely not going to be very high

Um, the facehuggers in AvP 2000 are an instakill.

Just pop 'em off with the pistol one by one or use jetpack to hover over them... Hate that gurgling noise they make as well.

Instakill but not ugly.

Alternatively of editing each map individually, you could mod them out existence.

Open GAME.CON with Notepad and let's try.
I won't be able to test it myself so backup the file first!

Since you don't like wet sounds, let's take care first of the Egg hatch.
Look for "actor EGG TOUGH". 13 lines down, delete (or comment //) "sound SLIM_HATCH".
If you don't want the Egg to ever hatch, delete "action EGGOPEN1".
If you still want the Egg to hatch, but not giving birth to a Slime, go down another 12 lines and change "spawn GREENSLIME" by "spawn RAT" or, if you still want some challenge, "spawn EXPLOSION2" or "spawn DRONE".

For some reason, I can't find the Slimer codes so it wouldn't take care of those directly spawned into the game.

Do what I did and map quick boot to mouse 2. Not q or anything else.

Now you can run around shooting while constantly kicking!