It is impossible for Ryanair to open MRS-BIA as all routes between MRS and Corsica are under PSO regulation.
But... if Ryanair want to operate to Corsica from BVA or GNB, no problem... except for the capacity that has to be found somewhere else...
This scenario is possible with a MRS based aircraft :
MRS-BVA-BIA-BVA-MRS
If they want to operate a GNB-Corsica flight they will have to get the capacity from STN or DUB (STN/DUB-GNB-BIA-GNB-STN/DUB).
Or....... they have to open a base in GNB.