The old plan called for replacing all of the bench walls along the length of both tunnels. Bench walls are the short concrete casements which house the cables needed to power the train and provide communications. Replacing them was necessary because of leakage to the cables which corrodes them. It would have been a total gut removal.
The new plan is to 'rack' the cables along the walls, which will improve access and be way cheaper. It's some kind of hanging cable system. Some of the bench walls are damaged, so they will be removed or patched on an as needed basis. Otherwise they are obsolete, so the important bit is that they don't fall onto the tracks. There will be sensors to monitor for problems with the remaining benchwall.
These techniques have been used in new tunnel construction outside the US, but never to rehabilitate an existing tunnel. It seems like a much needed improvement over the old plan which will have less costs and inconvenience.