Equip to TMT#002 Loki to keep spawning the illusions is gonna be my go-to.

wkD16-001 Martian Manhunter just found is new best friend

Pretty sure you con't combine the mirror with either of those effects. You can either get the Shape Change on a 3-6 OR regular Shape Change that generates Lokis or that heals MM, but you can't use both effects. See below.

Scenario: You equipped this on NFAoS Nighthawk Prime who has 2-3 friendlies adjacent to him and he is attacked. With his President of the United States power (see quote), does his SC succeeds also on a 1 or 2, even when the Mirror is destroyed?

Or does he have to choose whether to use SC Mirror version or SC POTUS version?

That would fall under

I don't think the rules section quoted is applicable here.

You choose to use the Mirror's SC instead of Nighthawk's.
Nighthawk says
"Nighthawk can use Energy Shield/Deflection and Shape Change. When he uses Shape Change, increase the result by +1 for each adjacent friendly character".

Because the lines are separated by a period, the effect from Nighthawk can be applied to the result. This will not change the result of the die roll and if you roll a 1 or 2 you will still ko the mirror even if you succeeded your SC.

Now if Nighthawk's power said something like,
"Nighthawk can use Energy Shield/Deflection and Shape Change and when he uses it, increase the result by +1 for each adjacent friendly character."

Then they would not work together.

So, is the consensus that you can't use this with ANY Shape Change specials? (looks at AVAS Loki longingly)