Levitation, Partial lift and lightening the load Options

[ialdabaoth]

Is levitation all or nothing? i.e., can it lighten something before it gains the ability to fully lift it?

For example, is it possible to use a low-force levitation spell on a very heavy object, to lower its weight rather than lift it? I.e., if we're in an 800 ton T-bird that needs to be lightened by 75 kg to make it over the next ridge, and everything that isn't nailed down has already been thrown out, could a Force 3 levitation spell be cast to help keep it aloft despite the blown rear vent?

Likewise, could a Force 2 levitation spell be used to lighten an ork just enough that they could walk on a broken ankle without putting too much pressure on it, like a crutch? Could a Force 1 levitation spell be used to make a boulder, already slipping slightly, JUST light enough that it breaks ground pressure and starts sliding down the hill? Or to provide the tiny extra 'oomph' necessary to help six trolls lift an overturned bus?