you basically have to increase your planet gra radius size, which you have to experiment.

let take this as an example:

moveAreaRadius 40000.000000
hyperspaceExitRadius 30000.000000

I am guessing that the build radius for any building is roughly 90% of the hyperspace radius, so if you mod the hyperspace radius you should be able to change position of the placement.

as for your first question, no, if you deviate from your first homeplanet, the planet you change your home to won't be modified at all