So: If one desires to bend or otherwise re-form an item made of aluminum alloy while retaining its strength, how is it done?

It would depend on what they actually use. If some of the strength comes from cold working, there's really not much you can do to reform while retaining strength. You could anneal and then form it, but strength would be gone. If it's a heat-treatable alloy, you could anneal it, form it, then re-heat treat it. For practical repairs, just re-form it and if it breaks, it breaks.