We will change the registration of our

You need a geometra who can sort out a new planimetria, and while you are at it get him to do the APE, s that also requires a planimetria.  

Assuming that your old stone house is registered as a house, it requires an energy certification (since 2014) and this now requires the submission of a planimetria 'stato di fatto' of the house.  It means an attestazione di prestazione energetica, basically, hiw energy efficient is your property.   If there is no planimetria lodged at the comune, then its pretty cut and dried.  If there is one and it differs from the stato di fatto, then it can open up a can of worms.  All of this depends on the current catastal class of your house, because making it into a house whenit is classed as something else will require paperwork and the payment of fines if the work was done without the necessary documentation

Thank you. Our house is registerd with the following categorias in the "Visura per soggetto"A/2 Abitazioni di tipo civileA/3 Abitazioni di tipo economicoC/3 Laboratori per arti e mestieriAny thoughts? Espen

If it is a second home and you are not resident in Italy, it will be cheaper to leave it as it is.  What you are planning is a fusione which will make all your separate properties one single house, and which increase your rateable value hugely.  Unless of course you have been told that you must reaccatasto it all because you have had work done,

Hi,if you need help, you can contact me to the following address: info@gmlegalservices.co.uk and I will be happy to assist you.Kind regards,Francesca