So I've made a map I'm quite happy with except for one issue; the legend is slightly obscuring it. If I could increase the size of my map by a few squares in one or more directions I could solve this problem.

Maybe I'm just being dense, but is there a way to do that?

I've tried increasing the width and height by editing them in a save JSON file, but it seems like some of the map assets are stored in a way that is dependent upon the height and width, so changing them screws everything up.

Is there some way I can change the size of my map?