This is Netreps ruling

There are 3 restrictions on changing a monster's battle position. You cannot change the battle position of a monster on the same turn it was Summoned or Set. You cannot change the battle position of a monster after it attacks. And you cannot change the battle position of a monster after its battle position has already been changed this turn.

All of these restrictions only apply to your free once-per-turn battle position change. In all of these cases, you can change the battle position of a monster using a card effect such as "Bite Shoes", "Book of Taiyou", or "Book of Moon."



So, if Book of Moon is used on it the turn it is summoned, then you cannot change the battle position since, if it was face up ATK when summoned, you already declared that its position for the turn is going to be face up ATK, which used up your position change. Same goes for if it attacks, even though you DIDN'T manually change it already that turn and, obviously, if you change it from ATK to DEF, then you can't change it back except through a card effect.

So it all depends on the situation.

If it is still your Main Phase 1 and you didn't manually change the monster that turn or didn't summon it that turn, you CAN change its position after Book of Moon is used on it.

If it was either summoned that turn or already manually changed, you cannot change its position that turn except through other card effects.

Switching card positions because of effects do not mean you used up the position change for that turn. Unless the card has an effect saying they have to stay that way for the turn or something similar like

Curse of Fiend
Normal Magic
Changes the battle positions of all Attack Position monsters on the field to Defense Position and vice-versa. These positions cannot be changed during the turn this card is activated except by the effect of a Spell, Trap or Effect Monster Card. You can activate this card only during your Standby Phase.

now I'm REALLY confused. Some say yes, some say no...im suprise no one said yes AND no yet...

ok here it is plain and simple.

If the battle position has changed (by any means, manual or effect) then you can NOT manually change the battle position again.

Face up defence to face down defence (via book of moon) is not a battle position change.

If TER is on the field you can not manually change the battle position (including flip summoning a monster).

Spot's Knight