if you are talking about the angle of the two pipes going into the coupler i would cut the pipe as close to the coupling on the BD side as you can and then cut the pipe on the other side far enough back to give you some working room... then i would take a length of pipe longer then the distance between the two... with that length of pipe i would heat it and then bend it to fit the angle needed for it to fit between the existing pipe and BD location.. once you have the angle then trim the pipe to fit and glue it all back together...
i would not use a Fernco underground and i would not use the coupling you listed if it shifts you will have issues..
Three may keep a secret, if two of them are dead. - Benjamin Franklin.
you cant fix stupid no matter how hard you try.