I have another style of LED fitted less than 12 months ago and with some help from the forum and fitment of diodes, yes, the twin amber lights can be used as reverse lights. I also had to fit a different flasher can or relay unit, as the new led's do not draw enough current to activate the original. Does not affect flasher unit when led's are fitted to trailer (as was the intended use) as the vehicle incandescent lamps still draw enough current to activate the flasher relay.
Do a search on previous post using led lights as a search word. I think August 06, 2007 was one post regarding this.