The luff rope of hanked on sails is normally too large to fit in most foil slots. Therefore, the luff rope must be removed and a small diameter luff rope installed. This is normally accomplished by trimming off the luff rope and sewing on luff tape containing a smaller (usually 3/16") luff tape. This luff tape is especially made for this purpose and little, if any, sail area is lost.
If your sail goes all the way to the masthead you will have to shorten the sail by about three feet in order to make room for the drum, top terminal and provide room for installation. This is usually done by cutting off the peak, and then tapering the top of the upper portion of the leech to restore the triangle. Any furling system utilizing foils necessitates sail shortening if the original hanked on sail fills the fore triangle.
You should also sew UV protection along the leech and foot of your sail. This will greatly prolong the life of a furled sail.
These sail modifications are a routine job for any competent sail maker.