Can you scale a custom 3D print up or down?

Often yes, but scaling is not a trivial slider that leaves everything else unchanged. Changing scale can affect structural stability, print time, surface quality, wall thickness, visual balance, material consumption, and final cost. Some models scale beautifully. Others become less practical or less convincing outside a certain range. So yes, scaling a custom 3D print is often possible, but it should be evaluated in relation to the object itself and not treated as an automatic guarantee. That is especially true when the request is functional rather than purely decorative, or when the requested size pushes the object far beyond the proportions it was initially designed for.