This mod allows you to add a new crafting request to the existing crafting queue
(For example: you have already added 5 inserters to the queue, then added some locomotives and also 10 more speed modules, but only then you realized that you need total of 6 manipulators, and by default you have to add them to the end of your crafting queue. It's very cool, but really slow).

With this mod, you don't have to waste your time while waiting for previous crafts to be completed and you don't have to cancel the whole queue in order to fill it up again.
Just press alt+left_click to insert one item in an existing queue, or alt+right_click to insert 5 at once.