The point of changing only one string is that you can use the regular fingerings--particularly the D, Dm, A, Am, Dm7/4-string barred G, and slide them up and down the neck--you can also play a lot of melody type stuff, either using scale fingerings or (especially effective) out of chord positions--

Just try a little experimentation--play a D and run it up and down the neck--do the same with the Dm7 fingering--if you get brave, slap your index finger across the 4,5,6,and 7 strings and hit the E string on the 10th fret with your pinkie:

0-0-7-7-7-10

now play a scale by playing extensions beginning on the 5th fret--

Does that make you happy? You've got enough there to keep you busy--fool around with it for a while, and in no time, your imagination will kick in--