to restore gdfs:
download setool
and when you open it press read gdfs, then follow the instructions on the screen (if there are any)
unlocking:
download any cid52 generic main (i reccomend r8ba024) and any fs (almoast 99% fs have english in themselves- if not all), and i don't know which custpack you have to download
ofcourse download k810 main and fs -k810 is the same like k800- but you get an option to patch and everything
download the patch i gave you (if you have downloaded r8ba024) to unlock your phone
and then download jdflasher and look at this tutorial
that would be all, if you use unlock patch- you can be 100% sure you can put any sim card in your k800
you can't kill your phone- it is very difficult
good luck, i hope i helped:)