Any icons that are on the toolbar but cannot be displayed, can be accessed via the “continuation arrow” on the righthand side of the screen. Can this arrow appear on the left hand side instead, so the first icon is displayed on the right and then the rest continue to the left. I can explain why if required, but I thought I’d just keep the question simple. I know you can re-order the icons, and I’ve done that but it doesn’t solve the issue I have.
This is not good. There are several reasons why. And most important is: your reason may change the resolution. E.g., you tell “I’m doing some work for a RTL environment”; and then the search will be in the “use RTL UI” direction. Otherwise, the answer would be “No way”.
I have 17 icons displayed and their text descriptions, so they can’t all be displayed on the single toolbar. My mouse is in my right hand = most natural / home position of pointer is on the lower right of the screen 
I’ve re-ordered my Most Used Icons ( MUI ) in Libre Writer so they appear on the right hand side of the screen 
This means pointer has far less distance to travel ( vertical move up 
). If MUI were on the left of the screen, the pointer would have to travel diagonally across to the left 
).
However I use two monitors with different resolutions ( 1920x1080 ) and ( 1680x1050 ) and use Libre on both. Only one monitor can show my MUI correctly ;
Option 1
Monitor 1680x1050 - MUI on the right hand side of the screen .
Monitor 1920x1080 - three rarely used icons now appear on the right hand side, pushing MUI 
towards the middle of the screen.
Option 2
Monitor 1920x1080 - MUI on the right hand side of the screen
Monitor 1680x1050 - some MUI now hidden ( accessed by the continuation arrow 
).
If the icon order was right to left , with the continuation arrow then on the left, my MUI could be at the top of the list, and therefore always appear on the right of the screen , regardless of screen resolution.