Replacing a constant string

Hi,

I have been searching the archives for this, but how can I replace the
value of a final string in a class with bcel?

Some background: I need to write a tool that replaces all strings A with
B in a jar file (f.ex. for changing network address).

I can iterate over all constants and find the constant I want to change,
but how do I modify it and save the change back to the class file?

Thanks
-- 
Per Thomas