Hi,

When you graft you are not changing genetic characteristics of
either one, rootstock and scion. Only in hybridization you can
change by combination of both. So each one will stay as it is in terms of what genetics gives them. That means if the scion is less tolerant to cold will stay less tolerant to cold.You possibly can find scientific literature about this in the internet or library.Or you can ask a person with a degree in these matters.Jaime.

When you graft you do change the characteristics of the scion. Of all the stocks for citrus trees, trifoliate is the hardiest, and it does impart to the variety grafted upon it some of its hardiness and its resistance to both heat and to cold. The imparting of resistance to heat is quit as important as its imparting cold resistance, for if the tree responds to heat by starting to grow, it becomes very tender. The measure of a variety's hardiness is frequently its resistance to high temperatures by remaining dormant. While it should be borne in mind that the place of union between the stock and cion is the one point in the trunk of a citrus tree most sensitive to cold, still this point may be protected and thus a distinct gain is made in the cion's ability to withstand low temperatures. Besides imparting to the cion some of its ability to withstand cold, it has a tendency to retard growth in spring. Trifoliate is extensively used around the colder parts of the Gulf of Mexico as a stock for Satsuma Oranges. No doubt it has been used for ages by the Chinese and Japanese as a stock for citrus trees to impart cold hardiness. The difference in resistance cannot be stated in so many degrees of temperature, because it is variable, and in no two cold periods or in not two locations would it be the same.