There are a few things going on here, which you are asking about. While I am not familiar with the specific operating rules that govern that particular stretch of track, I'll explain it as I understand it.
First of all, basically any train can be reversed. If there is a locomotive on either end, obviously the engineer can change ends and run from the former rear end of the train. With a conventional train, which has the locomotive on the head end, the engineer can operate from up there while someone, such as the conductor, visually protects the movement from the other end. In this respect, the movement would be no different than any other shove, such as in a yard or terminal area. Usually speed limits for shoving are 20 mph for freight equipment and 30 mph for passenger equipment. Of course, if any more restrictive speed limits are in place in the area in question, those would have to be observed.
On a main track, you add a few more variables in which complicate the possibility of making such a movement. Trains need some sort of authority or protection to operate on a main track. There are two types of authority, directional and bidirectional. In CTC, bidirectional authority would be something like Track and Time, where directional authority would be what the signals indicate. Under bidirectional authority, a train may move either direction within the limits of that authority without needing any other permission. Of course, they still need to observe the rules for shoving equipment, if that is the case. Under directional authority, things are a little different. Moving in the direction opposite the authorized direction requires permission from the train dispatcher, and usually such movements are made at restricted speed. Some signaled railroads allow a movement opposite the authorized direction without permission as long as the rear of the train stays within the same signal block, but some require permission regardless. Of course, if equipment is being shoved, all the rules governing shoving must also be considered.
In CTC territory, this can get confusing sometimes. The dispatcher controls "controlled signals," and it is those signals that grant authority to trains. The intermediate signals, while they do give information about the track and signals ahead, they do not grant authority. So if a train begins moving opposite the authorized direction with the appropriate permission from the dispatcher, and they then pass a controlled signal displaying a proceed indication, once they pass that they are no longer limited to restricted speed, because that signal authorizes movement in the direction they are moving. So the train may be physically moving backwards, making a shoving movement, but is moving in the authorized direction. Presumably, in the situation described in this thread, they would eventually stop, crossover to the other main, and move in the original direction again. Once they stop and start moving the opposite direction, they would again be moving in a direction opposite the authorized direction, until the locomotive passes a controlled signal displaying a proceed indication, and would be required to move at restricted speed up to that point. The direction the train is physically facing has nothing to do with the direction of its authority, which is where most people get confused. For normal, over the road operations, a train will be facing the direction in which it is authorized, but when you start to get into unusual situations or work trains, that goes out the window.
Current of traffic is a little different. It is basically two main tracks which are only signaled for the normal direction of travel on each track. When running against the current of traffic, you would not see any block signals, so you would need some sort of written authority, like a track warrant or track permit, for example. Since there would be no signals governing that movement, it would essentially be like operating in dark territory, and trains would be limited to 49 mph for freight and 59 mph for passenger. As always, more restrictive speed limits would also need to be observed.
Anyway, as I said, I am not familiar with the specific territory in question here. There probably are more local rules and practices that I am not aware of. But what I do know is that such a situation is not impossible, but it covers several different scenarios all rolled into one.
