64 only means "@" in the context of a string
of characters. wanting to exchange a byte's
value from "@" to "/" only makes sense in the
context of a string of text. a .zip archive's directory
entries can be read as text, and you can get away
with changing any "@'s" you find there to "/'s", but
changing values in the archive's headers and
compressed data, would corrupt the file. a byte
with a value of 64 means one thing in one context
and another thing in another. if you're looking to
speed up the corruption process, you can probably
pick a single random byte near the start of the file
and change its value. that should be enough to
do it. no need to change all matching bytes.