My best guess is that it only applies to site that is "current" when the uruk is played based upon the snapshot idea associate with other cards such as Eregion's Hills (only the minions roaming during the maneuver phase when the card is played are affected. It would not apply to a minion that was made roaming during say the skirmish phase as RB Rangers used to do). So, were someone to swap the site after the uruk was played and his text applied, the new site would not gain the keyword.
As Sgt points out, this question is essentially academic if one is concerned with using Balrog, DoM.
Yeah, I completely brainfarted about the balrog haha.
I thought about bibfortuna's golden rule of "Cards do what they say" and tried to follow that to its logical conclusion. I guess it could be taken both ways, but after reading through the card, and some other cards fully, here's the way I took it.
1. Uruk is played, Uruk makes the fellowship's current site X until the end of the end of the turn.
2. The fellowship's current site is X.
3. Site is swapped for another site.
4. The new site is now the fellowship's current site.
5. The fellowship's current site is X.
Take your example with
Eregion's Trails. When the card is played then, until regroup phrase, it will target all roaming minions at any point in time, right? So be checking. Is this minion roaming? Yes. Then is it strength -3. Now he is not roaming, he is not strength -3.
If we were to use
Eregion's Trails as an example, then we should apply the same thing to
Uruk-hai Scout. Is this site the fellowship's current site? Yes. Then it is X.
The flipside to this argument is that when it says "fellowship's current site" it's referring only to the site that the fellowship is standing on now.
Well...
1. The card doesn't say that.
2. In FOTR whenever a card is being singled out, it is usually "spotted".
Look at
Uruk Cavern Striker, for example. A single site is being targeted, thus you "spot" that site.
The way I now understand it after looking at all of this is:
If the card was to
only add the keyword to the site that the Fellowship was standing on at the moment
Uruk-hai Scout was played, then the wording would have to be as such:
"Spot the fellowship's current site. That site gains that keyword until the end of the turn."
This way you
actually are singling out the site that they are standing on at that moment,
so that if the site were changed in maneuver, the fellowship's current site would no longer have the keyword.
Hopefully bib will swing by to lend his knowledge...