As part of a journey from Martigny to Paris, via Lausanne, the first part is an International extension ticket. the connections at Lausanne are very tight and I would like to get an earlier train for the first leg from Martigny to Lausanne, to give a longer change time. Does anyone know if the extension ticket is flexible. (ie buy the 8.48 from Martigny but travel on 8.15 from Martigny to connect with the same TGV from Lausanne)? Thank you