If your wheels are both the same then you will not need to have your rear deailleur adjusted when going from 1 wheel to the other. If you have 2 different wheels then you may or may not need to have your rear derailleur adjusted. Take both wheels to your LBS and have this tested to see what - if any - adjustment you need performed. Make sure the mechanic shows you what you need to do. You are not dealing with a issue going from 23t to 26t unless your chain was cut too short to begin with. What you are most likely dealing with is 2 different hubs manufacturers. If you have 2 of the same brand hubs then you might need to adjust the spacers/axle.