Thanks for the comments. Its always nice to know why a feature will be used - to know how Sigil is used since I don't use it as heavily as many of you do, and to help with how to code it.
I guess something a little fancy will be required
I'm not too keen on using regex in the renaming - seems like overkill.
Is there any need to have the numbers in the middle of the name - or will they really always be at the end? If at the end as I suspect, then I can just provide a text box for the Starting Name, e.g. (Section0001) and use the number of digits at the end to determine leading 0's.