Soul Exchange,
Last Will and
Return from the Different Dimension cannot have an additional activation, or else it could be negated by an effect when it occured.
It is nothing more than resolving the complete effect of the card.
Soul Exchange allows you to tribute your opponents monster. When you finally decide to do so, that doesnt activate
Soul Exchanges effect, it just resolves it completely. If you never tributed a monster during that turn, then the effect would
Disappear.
When
Soul Exchange resolves, it is only the card that resolves, not the effect because you have not used it. All you have done is placed a condition for anytime a monster is tributed, which will or will not happen, based upon the turn players actions.
Last Will is the same. If you never send a monster to the Graveyard, the effect of
Last Will never resolves, and
Disappears.
Return from the Different Dimension summons a group of monsters that are removed from play at the end of the turn. There is no activation at the End Phase. The complete effect of RftDD is to summon and remove. What you do with the monsters in between is up to you, but the effect "condition" is in place until the End Phase of the turn it was activated.
If you place the monster(s) face-down, its no different than a monster summoned by
Summoner of Illusions, that is placed face-down. The effect condition is reset.
You can have an effect that has a lingering condition that ties in with the effect.
RftDD -
1. (Effect) Monsters are summoned from RFG.
2. (Cost for Summoning) Monsters will be removed from play at End Phase.
3a. (Lingering Condition) Face-up monsters summoned will be removed. Monsters placed face-down after summoning will remain.
3b. (Lingering Condition) Everything else that resets a condition...