Some insurers can get funny but this is nothing to do with the tyre you fit. If you get a new set of rims to fit the winter tyres to, this is where the problem occurs as you have effectively 'modified' the vehicle. Basically fit the new tyre to the existing rim or get an identical set of rims to save changing tyres.
Also I personally wouldnt fit winter tyres just to the front, (or rear, which ever are the driven wheels), you will upset the balance of the vehicle's dynamics. Effectively you will have more grip at the front, (or rear), the you will at the rear, (or front!), in a given weather condition.