yank out MS certificate ?

[vinifera]

since I'm moding my own win7 for home use

some files seem to need valid certificate or else installation breaks (since its moded )

but doing google, sure i find easy tool by comodo (kSign)

but every tutorial i stumble upon doesn't show how to get certificate or PFX out

of your own OS

 

and NO, i am NOT interested in downloading half gig of winSDK for some test mode cert

 

so as title says how can I yank out MS certificate from own system files and re-use it ?