Was thinking of buying a custom exhaust that fits a mk1 skoda fabia vrs and i was wondering if it would fit a standard mk1 fabia TDI

1.4 tdi?

Never looked at those but pretty sure it's going to be a totally different turbo position so I can't see a VRS system fitting from turbo back.

If the exhaust is cat back all you would probably need would be a reducer to go between the two different diameters of pipe,as I would guess the custom VRS system will be 2.5 inch which will be bigger diameter than the standard 1.4tdi down pipe

You'll also lose some torque low down and won't get anything extra at the top end so really not worth doing for performance, you could probably do a mufflerectomy if you want it noisier.