Windows 7: How to change Disk Signature to GUID - DiskPart refuses to obey

My WDC HDD is shown by DISKPART as UNIQUEID DISK ID=000FA830
DISKPART is able to change this to UNIQUEID DISK ID=000FA832

This shows that it works to a degree, and I understand and control it to a degree.



Unfortunately DISKPART is broken and lies when I change to a GUID.
e.g.
So far as I am aware I have used the correct format and specified a GUID that I found in Microsoft documents.

MY REASON :-
My WDC HDD was GPT style until a Linux Boot FlashDrive launch and abort followed by my controlled reboot into Windows.
The WDC HDD then had a new DISK ID of 000FA830,
and the first two partitions were RAW,
and the main partition which held Macrium Reflect Partition Image backup files became unallocated.

A Data Rescue utility has rescued every file that was in the main partition,
and all Macrium files less than 2 GByte in size are validated by their internal checksums.

The more recent 6+ GByte files are corrupt even though they are exactly the correct number of bytes in size.
I suspect that they were fragmented before disaster and the Recovery tool has put the fragments in the wrong order.

I am hoping that if the DISC ID indicates that it is GPT to the Data Rescue Utility then it might have a better idea of how to connect the fragments.
N.B.
There is only one 6+ Gbyte files that was not backed up to an external HDD,
and I would rather live without that file than pay for more software or learn Linux.

More details of my horror story are on
How can I protect my Partitions and files from damage

Regards
Alan