Remember to post questions in the questions section.
And, your sentence makes no sense whatsoever.
HxD is a Hex Editor.
When the Zone of a MW2 Fastfile is extracted, you can open the zone up in HxD, in order to see the Data in Hex(on the left side) and the data in ASCII(right side).
You can edit the data, in order to change the way the patch works. There are many tuts here on how to do that...

~tokzikate