If you prefer not to rebase your models, just assume that the model is mounted on a base of the appropriate size when setting the model up, moving it, or measuring any distances in a matched play game. For example, if you are a veteran player using an old unit that is mounted on 25mm square bases instead of the suggested 32mm round bases, you should set the unit up, make any moves, and measure all distances as if they were mounted on the larger 32mm round bases when you play matched play games. Although this may sound a bit complicated, in practice it is actually very easy to do.