Insert factory quick buildorder

Keyboard shortcut key

You can Quick-Insert a build order for a unit in an existing factory build-queue.
This way, you don't need to erase all previously queued units. You can even use this with Factories that are on "Repeat".

Use ALT and left-click on the unit you need.

The factory will produce that unit next, only once, and then will continue with the rest of the queue. Very useful!