Most mountain cranksets are available either with MTB or hybrid/trekking rings. The crank arms are identical. So you can just buy the other version. You don't even need to change the left crank unless it's a different color.

Square taper cranks, you need to worry about spindle length, but hollow axle cranks have their own spindle, and splined spindles have limited sizes and you're likely to have the right one.

A few weeks ago in that thread about 520 vs LHT, we noticed that with the 11-36 cassettes, one shift lower in the back, Surly chose to go one shift higher in the front by switching from hybrid to road rings. The bottom gear remained about the same and the top gear went up a shift. Why they'd go up one shift instead of down one on touring bikes is a mystery to me.