magical arm shield

[1cup]

like decoy dragon, when magical arm shield is activated, there is no replay, correct?
and when opp's monster is taken, it's battle position cannot be changed (while being taken- e.g. i take opp's ATK-pos Dragon Ice and put him into DEF-pos), correct?

Decoy Dragon
Effect Monster (Dragon / FIRE / 2 Stars / ATK 300 / DEF 200)

When this card is selected as an attack target by your your opponent's monster, select 1 Level 7 or higher Dragon-Type monster from your Graveyard, Special Summon it, and switch the attack to that monster.

Magical Arm Shield
Normal Trap

Activate only when your opponent declares an attack while there is a monster on your side of the field. Take control of 1 of your opponent's face-up monsters, except the attacking monster, and this monster is attacked instead. At the end of the Battle Phase, return control of this monster to your opponent.

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[Entropy]

There's no replay, and you can't change the position.

For the first, the simple answer that everyone can agree on is that the attack is redirected, which takes the place of a replay. For the second, there's nothing that says that you can switch the battle position, so you can't.

 

[1cup]

upon having magical arm shield take an opponent's monster (say, dark magician)
if dark magician were then to be flipped face down (say, book of moon)
when dark magician is flipped back up, would he return to his original owner's side, or stay on his current side?

 

[Entropy]

He would return to the opponent, similar to Brain Control. It doesn't matter if he is face-down or face-up.

Of course, if Dark Magician is flipped face-down BEFORE Magical Arm Shield resolves, then Magical Arm Shield has no effect (since the targetted monster is no longer a valid target).