Hi,
I've used QGIS to modify a SELAFIN after it was generate by BlueKenue. It works great ! Be careful, all variables will be deleted.
I have not yet tested BASEMesh to generate a SELAFIN (tuto:
hydro-informatics.com/numerics/basement.html).
I've spoken with V. Cloarec who implement mesh read and write in QGIS and it's not (yet) possible to create new variable and map values on a mesh in QGIS. It could be possible using C++ API.