So all the lock bits and fuses can be changed by high voltage programing?

I was thinking enabling lock bits and some fuses to avoid the code from modifing. Then, I noticed that this protection can be removed fairly easily by using some high voltage programmer such as dragon...

Does this resume lock bits operation automatically erase the corresponding flash region and still can protect the code from being read or it simplly removes the lock bits restriction and leaving the code there in the flash?

Yes, but it also deletes the code.

Yes, but it also deletes the code.

I thought if one lock bit protect the flash, a regular way to remove the protection will force the flash to be erased first, but those high voltage programmers such as stk 5000 or dragon could do it in a better way by just removing the protection without erasing the code?

The lock bits can ONLY be cleared by a chip erase.