The first catenary of the project has been erected at Castlefield Junction (Not Deansgate Junction as I originally posted - That's somewhere else entirely.)
Update: I've now been for a quick visit to Castlefield and I can report that a very short length of catenary has been erected at the Deansgate end of the viaduct.
The wires run from Castlefield Junction, so presumably future works will not need any closures of the Warrington line, although they may require the power to be switched off - I didn't spot a neutral section.