Development of Creative Commons licenses

[wiki_tomos <wiki_tomos AT inter7.jp>]

How do I add a warranty for my work (or someone else's work)? 

It just ocurred to me that the last item on the CC-by 2.0 license says:
"This License constitutes the entire agreement between the parties with 
respect to the Work licensed here. There are no understandings, agreements or 
representations with respect to the Work not specified here. Licensor shall 
not be bound by any additional provisions that may appear in any 
communication 
from You. This License may not be modified without the mutual written 
agreement 
of the Licensor and You."

Does this mean that I have to prepare a written document and sign it with 
every user if I want to change the warranty/ liability part, and give extra 
assurance to licensees about the safetiness of my work?

Oddly, it seems as if things will be simpler if I were neither the 
author nor the licensor, but simply a third party offering a warranty to 
someone using another's work. In that case, I will not be bound by "the whole 
agreement" clause. 

Well, hope someone can tell me I'm wrong. 

Best, 

Tomos