I'm no real "perl monk" but I think I understand a little bit of the topic.

First a few question:
Do ALL your lines really like that?
If yes: Take instead of a regex an "unpack" to break the lines into pieces.
There are two reasons: Faster and easier to understand what is in the file. A regex dot says nothing about the structure at all. You will know when you have to change your script after having six month no look at it.

Then: Am I right, the line looks like a set of hex-numbers? You can convert them back from a decimal number to a hex-number in your $writehandle->printf with the appropriate conversion sign.

Does this help you to make your program working?

Regards
Leuchuk