> client
>   proc
>       Load()
>           var/savefile/load
>           load = new ("Save Files/[src.mob.ckey]")
>           load["mob"] >> src.mob
>           load["x"] >> src.mob.x
>           load["y"] >> src.mob.y
>           load["z"] >> src.mob.z
> mob/Guest
>   Login()
>       if(fexists("Save Files/[src.client.ckey]")) 
>           L.Add(SUPER_NEW,SUPER_LOAD,SUPER_QUIT)
>           var/menu = input("Character File Found.","[world.name]") in L
>           switch(menu)
>               if(SUPER_NEW)
> 
>                   var/skin = input("Do you want to make a new character?","") in list ("Yes","Never Mind")
>                   switch(skin)
>                       if("Never Mind")
>                           goto reload
> 
>                       if("Yes")
>                           Create()
>               if(SUPER_LOAD)
>                   src.client.Load()
> 
>               if(SUPER_QUIT)
>                   del(src.client)
>       else
>           L.Add(SUPER_NEW,SUPER_QUIT)
>           var/newmenu = input("Character File Not Found.","[world.name], \"New Player\"") in L
>           switch(newmenu)
>               if(SUPER_NEW)
>                   Create()
>               if(SUPER_QUIT)
>                   del(src.client)
>       ..()

If you want to try storing multiple characters for a single key, you'll have to create more directories for the different characters the player is going to make. Therefore, when saving or loading from a file, just enter maybe:

Before:
load["mob"] >> src.mob
After:
load["[ckey(name)]/mob"] >> src.mob
Etc.

Basically this will create directories inside the player's savefile (using the player's name after it's been ckeyed) to save the files.

Read up chapter 12 (i think) of DM guide.