I'm nut sure what are you saying, because in the comparison of the two photos I see that you can edit the location line in boths. Can you edit any other properties of the wall? Maybe it is locked.

The left-hand pic is my attempt to change a wall location line on an existing wall via the modify tool. You see the selected wall (blue, vertical in this view) and I'm attempting to click on the drop-down menu for location lines in the properties menu. But when I click that location line drop-down menu, no drop-down menu options appear. The only thing that appears is a single floating box which restates the current setting for wall location lines. ("Finish Face: Interior," in this case).

The right-hand pic is me drawing a new wall. A drop-down menu appears in the top center which allows me to select the wall location line. (Your arrow is pointing to it.) Oddly, the drop-down menu appears over toward the properties menu when I select the location line menu in the center of the screen. However, once I draw the wall using whatever location line I wish to use, I can no longer modify the wall location line. The only way to get a wall on the location line I want is to erase and redraw it.

Hope that clears up the situation. Any help is appreciated. If there's a location-line lock function that I need to turn off I've not found it yet.
Cheers, rsrdencsu

Ok, so work-around found. I can type into the text box in the properties menu and Revit autocompletes to any of the location line options. So I'm able to change my wall location lines without redrawing the walls. I still don't know why I don't see a drop-down menu though.

Sounds like a graphics issue. One of my users worksets drop down in the status bar) is blank until you click the down arrow...