I agree with what Glitch has said about not limiting Abe's abilities too much for the first part of the game, but on the whole I don't really think a lack of chanting would require the game to be changed that much. In fact, it might force players to use grenades, bombs, grinders and levers, adding to the tutorial element whilst maybe making the game a little harder
With regards to the mudokons in zulag 1 not being rescued on the way out, bear in mind that to free all 99, you need to retread most of zulag 1 for the secret areas after breaking back into RF. It wouldn't be too great a change to have all of the original muds still there for rescuing when you return.
Like people have said, this is a new game being built from the ground up- things don't have to be exactly the same! I guess it comes down to weighing up the pros and cons. On one hand, we get (in my opinion) a more logical and immersive story of Abe's journey, on the other a few tweaks would be made to slig and mudokon placements (might be underestimating the level of change needed there!)
I've always liked the idea that Abe has a natural aptitude for spiritual powers and chanting, but still feel its a bit of a stretch to assume he discovered these abilities in RF where he would have no idea what mudokons are capable of.
Him learning to chant/possess in Monsaic lines would sit nicely with this- I always got the impression that the ability to chant and open bird portals is something that would normally take muds years to perfect, and possessing creatures is a highly advanced and rare ability (hence why the other muds cannot open portals and rescue themselves/each other- never directly explained actually!).
Big Face would teach Abe his spiritual heritage, and discover that (due to his aptitude) he is an incredibly fast learner and able to do in a day or so what would take others years. This would help further show Abe's significance and special status with respect to his prophecy. It would even tie in nicely with Abe's ability to later possess scrabs and paramites in AE.