I keep one acoustic guitar (a regular dreadnought) permanently fitted with a set of high tension nylon strings. It is easy to do: you either need to use a set of ball-end nylon strings or tie knots in the ends of loop-end strings and slide on craft beads so they fit with the bridge pins. You may need to slightly widen some of the nut slots to accommodate the wider nylon strings but fit them first and see how they sit at the nut. If you do need to widen them use a small piece of folded fine gauge enery paper, take it slow and steady and regularly try the strings for correct fit (you can leave the strings on to do this - just slacken them off a little and lift them out of the slots and push them to one side - the bass strings should fit OK but you may need to do it for the treble strings, G, B, E). The sound of the guitar with the nylon strings will be a little quieter, more mellow and, to my ears, much nicer than steel strings. I use mine to play in folk clubs and the sound of the guita always attracts good comments.