I use this feature every battle/campaign. I will usually buy about 5 companies. Say 3 infantry, 1 armour, 1 Support. Then I will delete any platoons I don't want, and purchase those I want.
In the Deploy phase you can reassign whole platoons or individual units (but not individual HQ units).
I sometimes reassign a detachment of SPAAA units or armoured cars to my armoured company; a sniper to each of my infantry companies; and I usually completely reorganize my support company.
Under my support company commander I may put:
Field artillery
Engineer platoon
Anti-Tank sections
Armoured car platoon
Recon/scouts/patrols
Battalion transport (trucks, halftracks)
AAA
FOO
MG platoon
Must be cool to have a wish and find it was answered years ago!
Always do it to
Tank Co often has armoured cars or mobile AA attached.
Infantry Co if dont come with assign scouts ATR or the like to them, transport to sometimes.
Arty might get static AA attached