I think in Ukraine’s position, this wouldn’t be a good idea. They unfortunately need to keep to their agreements to keep the support of their allies. I think they’d be much better off to just not sign the agreement and let their European allies take over. Either that or sign something that makes Trump think he’s getting something when he’s really not (my understanding is that almost all of the rare earths now sit on territory occupied by Russia, so that’s likely to be what the original agreement was).