Using a "Regedit" kinda app i found what follows:
My Device\HKEY_CLASSES_ROOT - this seems to be the place were all the relations are stored...
Here I foud almost all the file extensions used in my device, and some i didn't even knew about..
\.bmp has the fallowing keys:
Name - Data
Content type - Image/bmp
Default - bmpimage
PerceyvedType - image
This configuration seems to be common to almost all extensions keys....
After this I found this in the same root
\DefaultIcon - the file were the icon is
\Shell - contains sub keys
\Shellex - not common to all the keys i've looked into
Under \Shell we have..
and the string value
Name - value
Default - "Windows\IA_Zip.exe" "%1"
this is from the zip app...
the "%1" part seems to indicate that with the main app also the clicked file should open....
This info has not been tested and , being this a regestry issue , I advise to be carefull with your actions...
Hope this helped