Today I tried uploading my ebook onto Nook but hit the problem they have a maximum file size of 20Mb and my ePub file is over 80.

This is because it has nearly 200 colour illustrations and maps but by replacing these with smaller black and white versions I can come under the 20Mb limit.
I did this by creating the new image files and then with the "Add Existing Files" button in Sigil I added these new files to my existing ePub. The new image files all had the same name as the existing colour versions so these would be overwritten as they were added.
It worked, but in order to do this I had to manually choose to overwrite each and every file and with so many my finger was nearly falling off at the end.

So, unless there is a simpler alternative to the route I chose, what do folk think of this idea. This is to have the option in the "Add Existing Files" dialogue window to have a third button added which says "Yes to All" so with one click, all of the files could have been replaced easily?
Oh, and hello to everyone - this is my first post.