On Mentor Expedition ,you can decide to force trace to gloss OFF/Partial/ON (F4).
Gloss off means that the trace you are routing can't "move automatically"(means best route and length or push), but only manually move.
If you try to route over a gloss off trace, this trace don't move !!
So in this case a portion of that trace is closs off the other not.
Yes, after you have all your traces done, in the routing mode, select all traces or just the trace you want to change, then select the "unfix" or "fix" button.