When selecting new blueprint contents with different size, automatically adjust grid center if obvious

[sparr]

If you make a 30x30 blueprint and put an absolute grid reference point in it, then you replace the blueprint contents with a 40x40 selection, the reference point will still be in the same position relative to the top left (?) corner.

I'd like to propose that this behavior change in a few specific situations. If the previous grid reference point was in the center of the blueprint on either or both axes, move it to the new centerline(s). Otherwise if the previous grid box was aligned with the bottom and/or right edge, keep it aligned there.