Regedit.exe file size has changed

Hi everyone

I have encoutered a strange problem with the Regedit.exe copy under
c:\windows file size, it has changed when I zipped it. I though first it was
a virus? after a scan, no it's not, this is good! I did try with other copy
of Regedit.exe under System32 folder, it works. The consequence, is, if the
file is zipped and changed its size then when we restore, the program file
will never execute, meaning, corrupted. Since I use the Regedit program
often, I know this is the one that its loaded at runtime from the Window
folder, I'm concerned about the consequence of it. I'm glad the Winzip
program saw that because they do check the file size before they proceed with
the backup and it will stop the backup with the file size error message. The
way I found that out it's with another zip program.
My question is if the file is corrupted, is it possible to reinstall only
that program file? I never saw that with Windows setup before, I doubt it.
And I know from regular backup it is not possible to restore a windows file
under its directory even with the administrator right.

Thank you