Are you intending to breed these rats? If you don't know the genetics involved and can't trace their lines, I wouldn't recommend it. However I believe Rex is a dominant trait, and if so the babies would be a mix of Rex and regular furred.
rex and hooded apply to two different features!
Rex applies to fur. Rex = curly fur, double-rex = patchy fur. Either of these with a standard baby is likely to produce rex babies.
Hooded is a marking! The markings that result will depend on what the mother's markings are as well.