I have an idea yesterday. Is it possible to change the style of Fabia rear glass with a mask which draw like the new design of roomster ? (the curve of the glass)

I think with a plastic mask i could draw the curve of the roomster design)

I think that it will be original and change the design of the rear side of the vehicule

do you mean the B pillare sweep up, you would need to get the plastic specially made, not sure if it would match the design though

Buy some black vinyl and have a go - you can buy some cheap stuff from a sign maker or maybe even Halfords. Just chop it with some scissors to start with then you'll be able to see how it looks.