should be against the rules and cause for automatic flipping of the alias.

There is no context in which doing so is necessary, and no context in which disallowing the practice would be an impediment to the free flowing speech and variety of opinions expressed on the board.

Absolutely.  Impersonating another to cause trouble is so wrong.  
skb

it should also come with a warning, that a repeat is a ban-able offense.

some very descernable method should be used to let all readers know this.

Perhaps a big scarlet A at the start of the name?

(By the way, I know one can tell by the lack of the envelope symbol, but that is too subtle.)

It's the old slippery slope.

If you allow people to use an alias, having rules about them just seems like way to much bother.

If the post doesn't violate the already existing rules let it stand. If it does pull it.

Hey, when someone goes to the trouble to ape your username doesn't that mean they noticed you, and isn't it a form of a complement?

Just trying to express another point of view, nothing personal, I didn't follow the original that closely.

When it's obvious, and when it could easily be seen by the person with the handle, and others, as demeaning, and when it is done to insult a third party, with the possibility of the third party, and others mistakenly thinking it is done from the original handle. That seems quite clear, and not slippery at all, to me.

If someone were to adopt the name "Helikoan" or "Hellikaon" etc it would be pretty obvious. And then suppose that user started hurling insults at other particular members, being generally misogynistic, or making claims that they demand extra time or like to slap providers around, etc. etc. then its being done strictly to make the true handle owner look bad and destroy their reputation on the boards and could be used against them by other providers they might want to meet. It shouldn't be allowed.

Remember, use it only for good, and not for evil

Hmm, maybe I should create all the simple modifications of my handle into aliases, to prevent anyone else from doing it!

... comes great responsibility.

Since I can't promise to use this "zisk." alias only for good, I will sadly have to relinquish control.  You may want to pick it up soon, before the Agents of Darkness realize that it is now again available and want to use it for their nefarious purposes.

I, briefly, thought about creating alias for multiple modifications of my handle, then decided that it wasn't important enough to bother.

(Now, I wonder what will happen when, after I post this, I delete the alias.  Hmmm ...)

if they are done under an alias or not.

Not to belabor a point, but I feel that if anyone did the things you mentioned, hurl insults, make up claims, harass, try to hurt someone's rep, etc, the post should be yanked.