Setup Symmetry
Setup Symmetry allows you to position and configure a 'symmetry node'. Once the node is set up, you can use the 1-9 hotbar hotkeys to switch back and start placing blocks with symmetry.
Setup
Begin by placing a node with right click
Add a 'flip modifier' using Ctrl+F
Add a 'rotation modifier' using Ctrl+R
The node can be removed at any time by pressing Delete/Backspace. The node can also be temporarily disabled by simply removing all the flip/rotation modifiers
Multiple modifiers can be used at the same time to achieve more complex symmetry
See below for a demonstration