You are free to remove TikiWiki and Tiki, Wiki, MyTiki change what you want.
grep -r "tikiwiki" *
just replace tikiwiki with the word you want to replace and it will list each file you need to change.
If you want to hide the fact its TikiWiki, remember to redesign all the CSS file to remove all the tiki- elements, and maybe also run the filename renamer to remove tiki- from each and every file.
There are tons and tons of Tiki- everywhere and if your honest with the client and say its a open source CMS which may contain bugs and problems, 99% of my clients are happy with that.
You cant say its your own work, remember that its Copyrighted by the Tiki Community, that is everyone who has ever submitted a line of code to the project! but you are free to remove all references to the words tiki, tikiwiki, blah blah.