I'm Gonna Wreck It!
Yes, they replace the respective T-Rex and Raptor tiles.
The T-Rex will move 1 space and eat 6 (instead of 5) dinos OR move 2 spaces and eat 4 (instead of 3) dinos.
The raptors still move 1 space and the other 1/2 spaces and eat 2 dinos apiece. However, now they will scatter 3 dinos instead of 2.
Basically they become more dangerous. Frankly in the games I have played, raptors and T-rex always seem to get taken so I have not seen the need to make them stronger but depends on the players.
I remember reading somewhere that the main reason they even exist was because the artist liked both drawings he had done and couldn't decide which was better so they were both included in the game without any real plans as to what to do with them. They came up with the rules for the "promos" later. (To our benefit)
However, I'm sure you could use the regular rules easily and just change tiles if you want to mix up the artwork