The following steps are taken to convert an Office GUID to its compressed counterpart:

Here is the uncompressed GUID for Office 2003 Professional.

{90110409-6000-11D3-8CFE-0150048383C9}

Here is compressed GUID for Office 2003 Professional.

9040110900063D11C8EF10054038389C

Here are the steps demonstrating how to convert the uncompressed GUID to a compressed GUID.

To convert this Office 2003 uncompressed GUID to a compressed GUID we will first separate the above GUID into 5 sections and drop the brackets.

90110409 6000 11D3 8CFE 0150048383C9

Next we will reverse the order of each of the first three sections.

90401109 0006 3D11

In the forth and fifth sections we will transpose every two characters.

Here is the fourth and fifth sections broke up to every two characters are separated by spaces.
8C FE 01 50 04 83 83 C9
Let’s transpose each section like so:

8C FE 01 50 04 83 83 C9
becomes
C8 EF 10 05 40 38 38 9C

Then lets put the it all together and remove the space 

90401109 0006 3D11 C8 EF 10 05 40 38 38 9C
becomes
9040110900063D11C8EF10054038389C

This is the logic behind how the Office uncompressed GUID is manually converted into a compressed GUID