Edit XML contents of gzip file

I need to make an application that can edit the XML contents inside a gzipped file.

Is there any software I can use that's cross compatible with Win/Mac that can do this?

• open the gzip


• search the xml file inside the gzip for a specific tag


• convert the contents of the tag from hex to ascii


• edit the ascii


• convert the contents back from ascii to hex


• save the xml file inside the gzip file

Any help would be much appreciated.