There are some possible reasons why the immunity clauses came up later:
1. The designers looked at it and felt it was necessary, unlike previous stuff, and thus they left previous stuff alone.
2. The designers actually realized players would do silly stuff like try to sack stats when they're immune to ability damage, so they added the immunities clause but weren't able to add such things to previous publications due to problems updating the material, and because of that they haven't also made a general statement regarding the issue.
You get the idea.
Alright, you caught me on whether the rules support my statement. At the moment I have nothing to back it up as far as whether it's in the rules. It's obviously common sense though.
And apologies if I come off as irritable, because I am. Stuff like this gets to me mostly because the person should know whether it's cheesy and thus bring it to their DM's attention to get the okay or no way. If it was simply an exercise in making a character that may or may not even be played, then that might be acceptable cheese territory.
As for the bit about replacing it with a different stat, it'd still be ability damage and since the character is immune to ability damage, it might not go through at all regardless of which stat is chosen.