Good point, Jim. Do whichever is comfortable to you, the player of the dulcimer.
Removing a Melody String - Which One?
I agree with JenniferC and Sheryl St. Claire. I remove the outer string, but for the same reason. Remove the one that makes the remaining strings the closest to equidistant especially if you play chordal style. It depends on the dulcimer.
updated by @jim-yates: 02/10/17 12:16:04PM
Just loosen the 1st melody string until you have enough slack to drape it down the side of the fretboard and out of the way. You can then try with just the 3 strings. If you don't like it that way, you can put the string back in place without havine to restring.
This is a genius idea!!!
It's easy enough to change strings that I'd recommend experimenting with which melody string to remove. Try it one way for a while and then switch to the other to see which is most comfortable for you. Why, you could even try different string gauges to see which one feels and sounds best on your instrument. Variety being the spice of life and all.
At Kentucky Music Week I observed people loosening the outer string enough so it could be pulled off the side of the fret board. I finally got around to trying it this week and I like the sound of my dulcimer better with three strings instead of four. I will probably end up just removing that outside melody string but I had no idea it would sound differently. Now it has more of the mellow sound I was looking for. I am a work in progress.