I did that with a lot of my son's clothes when he was growing faster than my budget could keep up. For example, I'd cut off his winter pajama pants to make summer pajama shorts, very similar to what you described.I still do that when I can. My jeans go thru a cycle, they start as casual wear, as they wear out I turn them into chore clothes, and if the knees get torn out I'll cut off the legs and use them as summer time chore shorts.