How to edit parts of registry files with restricted permissions?

Question

Windows

I immediately apologize for the crooked wording of the question, I don’t even know how to clearly formulate it briefly. In general, the situation is this: I installed Windows 7 on the second partition, but the system assigned the letter C: to it, although it is the second one. The first partition has Windows XP installed (don't ask why). I definitely want the layout of disk beeches according to sections to be exactly the same in both OSes, i.e. the drive on which Windows 7 is installed should be seen as D: from both systems, and the letter C: should be assigned under both systems to the drive on which XP is installed.
It is impossible to change the system drive letter by regular means, but you can boot into another system, open the registry with any editor that can load registry hive files and edit HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices (more details here).
But after that, a bunch of keys remain in the registry, in which the paths to files on the C: drive are registered. It is enough to do a search for "C:\" and there will be a huge number of results. You need to do a massive search-and-replace and replace all C:\ with D:\...
And so: with all hives except SOFTWARE and SYSTEM, this works, and in these two, rights are limited to most keys.
How to overcome it?
So far, I have some hopes for the Linux PCRegedit and the editor built into the PrimeExpert emergency boot cd (it is clearly written about him that he can manipulate the ACL), but you have to pay for the second one (which you don’t want to do, even though you need to do it once and don’t know will it help), and the first one, it seems, is deeply asleep in Bose - all links on the Web (I have already rummaged through everything) lead to the ISO-shnik on the official website, which died a long time ago.
In general, if anyone knows a way to bypass rights restrictions in the registry when editing offline and / or a program capable of this and can share a link - many thanks in advance.

Answer 1

Everything turned out simple. As the description of the Windows registry hive file format showed , nothing but the main file header is protected by any checksums, and therefore the replacement of lines of identical length with each other can be done with a regular HEX editor. The only nuance noticed is that the registry contains strings in both 2-byte Unicode UCS-2 encoding and in single-byte ASCII.
Nevertheless, although the problem is solved, if anyone knows more "cultural" ways, it would still be great to list them too.