About the wallet.dat file , there are keywords like "pool" , "name" , mkey, key! , ckey! , keymeta! and after the keywords is encoded data ..... I have tried to cut and past keyword sections of the file into another and it does not work. I would try to replace a "pool" section from one file to another and that basically just breaks your wallet. I think the keyword sections are linked in a way I don't understand. Maybe someone here can point to a page that explains that in detail.
The wallet file is actually a Berkeley database.
The keywords are the keys of the key-value pairs stored there, and some encoded data follows each key and value.
To decode them, a tool such as pywallet would be needed.