how to change image resolution without effecting scale within the image itself using gimp as in retaining the roundness of the moon
Remove the Moon to a different layer.
Scale the image layer.
Replace the moon in the image:
Make the moon larger (Scale it evenly 1:1 fixed aspect ratio), and move the layer around until it is where you want it.
As long as it covers the hole remaining from the original removal, all is good.