Mixing RAM modules 1Rx8 with 2Rx4 on T7810 server

Hello everyone, how are you? Hope you are well,

Context:

I would like to know if it is possible to upgrade a T7810 server from 16GB to at least 64GB.  

Current situation:

According to the server's official manual, the current distribution on the server T7810 is D16 which consists of 4 modules of 4GB:

[DOUBT] Do you know what the red cells mean? Are these red modules optional? 

In this server, all the installed modules have these features:

• Capacity: 4GB 
• Architecture (ranks): 1Rx8 
• Technology:  DDR4 
• Model: PC4-2133P-RD0-11 
• Frequency: 2133 MHz 
• Memory function: Registered 
• Brand: SK hynix KOREA  

So to make it clear, the D16 distribution on the server is:

Question:

I wonder if it is possible to buy modules of 32GB (https://www.dell.com/en-us/shop/dell-memory-upgrade-32gb-2rx4-ddr4-rdimm-2666mhz/apd/a9781929/memory

• Capacity: 32GB 
• Architecture (ranks): 2Rx4 
• Technology: DDR4 SDRAM 
• Model: DELL A9781929 
• Frequency: 2666 MHz 
• Memory function: Registered

And make the system work in a distribution of type D128a but using just one module per CPU:

I'm asking this because of the red cells on the official document (see image attached some lines above: for the D128a there are 2 modules in red textcolor) 

Extra mile:

It is desired to have at least 64 GB, but re-using the 4GB modules would be a nice-to-have, so I would like to validate whether a distribution like the following is possible or not: 

Note: Given the official manual specifies that modules will work at the least frequency installed, the 2666 MHz modules will work at 2133 MHz.

Thank you in advance for your help and answers.

Best regards,