It's a fair while since either GTE Baitrunners, or RE Baitrunners were available. However, there was a "special edition" RE Baitrunner 5-10 years back. I don't have any particular information on hand to give a definitive answer. However, when Shimano produce different models, that otherwise look basically the same, the differences usually come down to internals. Different numbers/types of bearing, different gearing etc. External/cosmetic differences are often marginally more obvious. Things such as different bail arms/rollers, different graphics and different spools. All metal spools, all polymer spools, stainless rims on polymer spools, different lips on spools, number of spare spools supplied etc. Occasionally, the material used for the body/rotor is different. However, IIRC, both the GTE and RE Baitrunners used XT-7 bodies/rotors.
I believe that there weren't massive differences between the RE and GTE. Minor things like steel lipped spools and number/type of bearing are likely to be the differences.