Dan the Firaxian only mentioned rules changes visa the .bic file, and is himself "techinically incorrect" in the effect that he is only thinking of a rules change, and is not addressing a major portion of available downloads that are indeed true mods!
What was not mentioned, is that a vast majority of mods actually do have changes BEYOND the .bic file... for example, terraign changing mods, ruler leader changes, etc, etc.
For example, a mod which changes a civ (lets say America) and a ruler (and his picture) to say Spain and King Phillip, will change the .bic file AND the graphics file... if you do a complete install of the mod, and do NOT replace the default .bic file, if you attempt to play the game with an original bic, but modified graphics, you'll get the graphical changes from the mod but the ruler and civ will be incorrect (it will say US and Abe Lincoln, but you'll still see King Philip of Spain).
There are other mods that change more than the bic file than just the Civ mods, but I think you get the drift.
Terraign mods are another example that rarely have anything to do with the .bic file, so sometimes changing the default bic files do occur in mods... that's why they're mods, not scenarios.
So Dan is only right if it's STRICTLY a rules changing mod, and nothing else, then yes, it could (and should) be loaded as a scenario... true mods though, often need to change the default bic, or you'll have funny results if you don't!
The Firaxian company line will always be not to change out the base files, but frankly, in any mod community, it's bound to happen, and such advice is about as important as not breaking "the seal" on your computer before making upgrades to the system. Bottom line, you have the original CD, so in a worse case scenario, you can ALWAYS go back to the original version if you forgot to back something up.
Firaxis will not encourage real mods, only the minor rule-tweaking "scenario" mods, but if you wanna make an omelete, you gotta break some eggs!
