The actual recovery.img like the recovery binary file, or a nandroid backup .img file. If your talking about the revoery image file, you can't decompile it. You can however download the cm7 source, modify the cwm recovery portion, throw in your own kernel zImage and compile the CWM recovery. Thats about it though.
If your talking about a cwm nandroid there is a toold called unyaffs that will break it out into files and folders.
But as far as the actual cwm recovery.img, you can't edit the binary once its compiled. And you have to compile it under linux or mac osx, so its not possible on windows.