Why hello there.
For all those here who thought about digging through the data stored in the myp files but couldn't be bothered to find out how to do it i have a short summary about that.
0) The file format
These files are basically a huge array of compressed or not so much zlib compressed (i.e. videos) files. Each entry is described with some basic info like file hash, compressed size, compression and uncompressed size to name a few. Apart from that the file has of course a header of its own and every 1000 records you have a fileindex entry.
If you want to know more about it than the stuff from my memory you can check this
or logfiles and sourcecode of the two tools i want to tell you about.
Not so much a usefull tool as a proof of concept you will reach it's limitations quickly, as it only recognizes 3 different filetypes and no filenames. An interesting project which doesn't seem to have that much attention lately.
More UI, more features, more bugs.
Today i found this interesting project on google code, written in c#, completely with sourcecode and the capability to retrieve filenames from hashes. It states to be able to add, remove and replace files in myp archives which i haven't tried so far, but since it is quite bug-ridden i would recommend anyone to make backups before trying. This pretty young program has it's own forums with no posts so far, yet i hope it's development will continue as it seems to be the most promising out of the two i found.
easymyp - Google Code
With possibilities like this emerging we will hopefully soon witness the birth of an active model editing scene and nude patches of course.