I noticed a Youtube spoof edit pitting Ewoks against the Predator.
It shouldn't work because they are very different kinds of trees but it kind of did.
Maybe there are other films where footage of forest of different types could be brought together to make the Endor moon a less Earth like forest by mixing incongruous foliage together.
Meanwhile here is another Briefing Room mockup.
Most of the Prune Faces hardly move so it maybe relatively easy to replace them with aliens that match the costumes and look less like really bad Palpatine masks.
If these were totally new aliens they could then be filmed and added to the Endor ground battle as they are clearly seen getting onto the Tydirium but are never seen again :
