A unit can be combined or divided during its activation and movement. To divide or merge a unit, it must move into 5 cm of another model or at least 5 cm away. A single model may never leave a unit, unless it is a character figure. A character or vehicle may be it's own unit. The unit has become engaged in close combat.
Modifiers usually count toward the final dice total for the action being taken.
If modifiers apply to a large group, it may be possible to spread the modifiers out across the entire unit. A model may move a normal move and fire its weapon. If a model moves it may not fire its weapon at close range. Any shots that would have been close range are now medium range. A model may Run by advancing its normal move plus 1D10.