Posters are plastered all over the metros and RER about RER A with only a mention that something is going on with RER C. Even at Gare d’Austerlitz the information is limited. With digging, I was able to find maintenance information about the other RER works scheduled. Use Google Translate to read the page.
I was heading to the Eiffel Tower (Tour Eiffel) area, for example. I took line 10 (Boulogne) to La Motte-Picquet-Grenelle, changed to line 8 (École Militaire). The search engine RATP journey planner suggests walking from La Motte-Picquet-Grenelle (16 minutes) to the Eiffel Tower.
RATP Visting Paris page in English provides travel information and a Next Stop Paris travel and advice application.
For the summer, add an extra half-hour to your journey in case of any surprises or “colis suspect” (suspicious package a voyager leaves behind and that must be blown up). On this RATP page (Pourquoi le trafic est-il perturbé en cas de découverte d’un colis suspect?) is a simple info graphic that describes why traffic is disrupted when a suspicious package is found.