My 16th 10 way edition consumer unit has 4 MCB's fed from the !00A main switch(for lights, etc.) and 6 MCB's fed from a 80A, 30ma RCCD ( for power, shower, etc.).
To update and comply with 17th edition regulations is it permitted to change the RCCD to a 100A,30ma RCCD to feed all 10 MCB's from the 100A RCCD by disconnecting the busbar feeding the existing 4 MCB's at present fed from the Main 100A switch and connecting it to the 100A 30ma RCCD.
Then all circuits would be protected by a RCCD device.
There is not enough room in the box to fit in a 2nd RCCD as well.