[Mobhack]

If you need a unit to fire in turns 1,3,5

select unit, advance firing to turn 1 with the + key, plot what and where to fire
now advance the + key to turn 3, plot what & where to fire
then advance the + key to turn 5, plot what type of fire and what is firing.

That should only fire the plotted batteries, with the plotted type of ammo, in those turns only.
The batteries will not be available to the owning player until the programme is completed (or the owner cancels all programmes with the appropriate key). No need for fiddling with reinforcements.

It is straightforward once you know what you are doing. Only way to redo a programme once you have decided you have made an error is to clear and restart though. Set yourself up a little test assault scenario with 2 or 3 batteries and play with that as a training exercise.