If you are using a Bowyer's knot at one end, then obviously, just tie that end up a bit shorter. If you have a double flemish or continous loop string, you can take up A LARGE amount of excess length by simply twisting the string up tighter. For performance's sake, you want to get a string that is the right size for your bow though. An overly twisted string is heavier than it has to be to do the job, ...and it stretches more as well. However; for finer adjustment of your bace height, say a couple of inches or so, twisting the string up or out should work well.
OneBow