I agree with the basic premises of décroissance (and I think that the outline you provided here feels better than the "charte").

I strongly wish to switch tomorrow totally to the agricultural model defined in the charter, and changes are already underway to do so; because a non-intensive agriculture will produce less than the one we currently have.

In my opinion, degrowth in general consumption (of non-food items) can make a much larger difference. This is touched several times in the charter, but never explicitly mentioned: build much less but more solid stuff. From computer printers to household applicances, the stuff breaks down (and is expected to break down) far too fast; and thrown away (because it's cheaper to get a new one than to mend it).

Further I disagree about not having to change the lifestyle. We need to consider swapping/mending/lending something as a first option and buying as the last, not the other way around. And, if we want to change the agricultural system, we will have quite another diet.

What does negative growth finally amount to, using the current benchmarks? Use less resources and less energy.   Means, that we have to find other benchmarks where we can "grow"; along the lines of becoming more efficient with less stuff available (Maybe Intelligent Growth :-p   ).