Right now when a factory is in a control group, any units built by said factory will inherit that group. You can then select the units in a group with one keybinding, and the factories in said group with another keybinding. This is neat, but I have some suggestions:
When a factory is assisting the build queue of another, the units built by the assisting factory don't inherit the control group of the assistee. When a factory is assisting another, have the assist-constructed units inherit the control group of the assisted factory, but have any "side project" units in the assister build queue inherit the the assisters control group (if there is one).
When a control group is set for units only (eg there are no factories selected when you press ctrl + num, in the default keybinding) don't strip the control group from the current factories. Likewise, if only factories are selected when the control group is set, don't strip group number from any units currently in the group.
(minor) Currently when you set the control group of a factory (even if it's to the same one, like when adding additional factories to an extant group) and a unit is being construction, that unit is stripped of its control group and doesn't inherit the new one. It would be nice if any unit under construction got the number of the new control group when the group of the factory is modified.
- assisting factories inherit control group
- changing control groups of units doesn't affect factories in the group and vice versa
- when the control group of the factory is changed, any unit currently under construction gets the new group