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As far as I remember, in Heroes 5, you can hold down Ctrl while clicking to attack, and they won't move.
Melee attack for ranged units definitely worked for me using this old method.
I tried it, but it doesn't work.
Added 3 minutes later
It seems that applying a second regeneration effect cancels out the first one.
If you apply a single regeneration effect on top of a general one, only the single effect will remain.
If you apply a general effect on top of a single one, the single effect will remain.
The effects do not stack.