If you insure it as an MP215 rather than as a modified ST it might not be as high? I believe the ABI code for an MP215 ST-3 is 18503399
And yes, it's an increase from 200bhp to 215PS (212bhp), so about 12 horsepower not 35. That's 6% versus 19% increase so could be part of the reason.
2005 Fiesta ST 182bhp
Milltek non-res, Newman fast road cams, JamSport map