I would like to see a detailed example of the exact situation.
The reason is that I'm not sure exactly what the OP has in this binary file.
See MAC address wiki for gory details

One common form of human readable text is like: 01:23:45:67:89:AB. In a binary form, that is 6, eight bit bytes (2 hex digits each) or 48 bits or 3, 16 bit unsigned integers. If that human form is stored as a string for easy output to humans, that's 17 bytes of ASCII plus probably a trailing zero. A binary file would typically just store the 48 bits (not a string).

You can use regex to replace one binary string with another binary string. However, I am not sure that is best here because we have almost no application details. I suspect that more code than just one regex will be required for a good UI - could be wrong about that - perhaps depends upon what is meant by "good UI"! There are also other possibilities in the menagerie of Perl options.

I hope the OP can show at least a partial hex dump of the file and then explain what he wants to replace with what.
And comment about potential CRC characters is spot on- probably don't exist, but they might.

I would be curious to know a bit higher level of the app like why a low level binary edit is needed?