Temporarily disable a symmetry plane
Sometimes there is a need to temporarily disable a symmetry plane to place some functional blocks that only go on one side of the ship. Currently we have to cycle through the planes with M until we find the one we want to disable, right-click, then press M until we are back to normal, place the block(s), then cycle symmetry planes again and fly around the ship until we find the exact spot again where it was before.
An alternative could be that we can temporarily disable/enable symmetry planes with something like Alt+N for X, Ctrl+N for Y and Shift+N for Z. That way we can keep our attention on the spot we are working on.
What if I haven't set any planes and press Alt+N? Either nothing happens or the game could create the symmetry plane for us at the center of the grid's bounding box. I think that's usually what you intended in that scenario.