The zipfile way to delete or rename would be to just change the index. It really doesn't want to be re-written as it is designed to span disks. Many old versions of files can be scattered within the zip. In addition self-extracting zip files will have executable code in the front of the zip. To make a zip smaller, it's desirable to have a filter function. There were points brought up about zip with overlapping data blocks (and you could envision saving space by having many identical files share the same compressed block... but this is not legal zip. A file info header block must precede EACH individual file data block. This is brought home by there being only a length field in the info header.