I was reading WBW Tutorial Scenario making, and to add more units in a group, he suggest buying sniper and "replacing" them by the unit you want.
Problem is the stats have to be adjusted (otherwise your new tank or gun as sniper stats: high for infantry, low for armor and artillery).
I do it this way:
1 - I buy more groups of the units I want than necessary.
2 - During deploy I reassign part of this surnumerous groups to their new HQ (to increase the number of units in the groups I want).
3 - I go back to the Buy screen and delete the half group remaining (the ones I used to dispatch their units to groups I want to keep)
So I do not need to remember fiddling with the units' stats...
Well, there are just more than one way to achieve the same goal...
Cat