I assume you got here through link in the word "codename" in Kasanova's description, so from that point:
There are a bunch of different Wizers, alternating pretty similarly to Undertale AUs, which, for instance, for Kasanova would be Underlust. It's often because they are indeed correlated to the universe very similar to the respective UT AU, but that's not always the case and sometimes they may not match the alternation rule or otherwise look similar to a certain AU character and not be from any extent of that universe. A good example of that would be Professor, who may be mistaken for character of the same AU from which Science Sans originates, but that is pretty contrary to that.

And since most of them know about existence of at least some others, to discern from each other they have codenames/nicknames, usually representing in English a word starting with a "C" pronounced as a [k] sound and replaced with letter "K", implying their last name. For that reason some Wizers treat that codename as their official surname and use it in their worlds, but that's pretty rare to see.

If you still struggle to understand what "alternating pretty similarly to Undertale AUs" mean, here some more examples: Wizer Kyborg or Klassic represents an "original" universe, hence Undertale; Kold lives in the universe in which everyone is a bit more ruthless or even violent and have more red colour in the pallete, simillarly to Underfell; Kaptain lives in universe in which almost all monsters are aquatic creatures, simillarly to Oceantale; and so on, and there are all of these "swap", "shift" and "change" versions, an infinite amount of them which makes naming them all pretty much impossible and the verses themselves repetitive, not much point in telling more than that his swap "pair" is his friend who's even more chaotic and erratically powerful.

I don't assume that Kast (Account owner and the one you'd probably call "writer") would let you play with most of them, and I specifically reserve my own right not to participate in that, so I don't see the point in making pages for any of them. A lot of them you'd probably wouldn't want to play with yourself, since mental health of most of them is far more damaged which makes them break the fourth wall more often and more unconsciously and that is to distress of plenty, if not vast majority, of roleplay writers. As you can see, some even write articles for Kast in your universe because he's too lazy to do it himself and it's easier for me to do it with my tools, that is how bad the fourth wall situation for some...