I haven't done this, but my former TW (SN 360) had received a C-fuselage when it was owned by Martin Heide, and I had bought it like this. Schleicher has issued a technical note on this (it's an approved modification), so best would be to talk to them.
You'll get the best of two world's - the advantages of the C fuse, and the 55 deg flaps. The C wins offer no advantage whatsoever.

Bert
Ventus cM TW