For the sails to be an effective means of propulsion they need to transfer a lot of force through the mast and stays to the hull. This require the attachment points to be very solid. Not something you can easily do as a retrofit. You'd need to reinforc the hull aroud the mast and stay attachments.

They likely can but with reduced changes for being optimal. Sails, keel and rudder should be balanced so that adjusted sails cause minimal pivoting force to mitigate with the rudder. Also the supports below the mast and plates for the stays likely need planning to allow sufficient structure without limiting the working angles of boom too much.