we have had users ask for terrain resizing before.
If we kept the same mesh resolution and the same blend map resolutions, then the size of the terrain could be rescaled and also rescale the height of each vertex to match, therefore it would look like a uniform scaling.
The only problem is if you change the resolutions, then there are more or less vertices/pixels than what you worked with originally.
I might have a go at the resizing though with same resolution.