Another strawman. There is absolutely no requirement for such a constraint.
To demonstrate the validity of the biological ID hypothesis, it is enough to point out that specific examples of intelligent design -- in the form of large scale biological changes --can and do take place, on a daily and industrial-scale basis.
Validation of a hypothesis is not verification, of course (you do understand the difference, I presume). One cannot simply brush off the scientific necessity of producing evidence through testing.
Nevertheless, your suggestion that the post-production detection of such biological efforts is scientifically impossible, and therefore not worth doing, is rather difficult to take seriously.
I accept Behe’s contention as being definitive, as he is the only actual Biologist to weigh in on the I.D. side that I know of. His I.D. hypothesis is that ‘The Intelligent Designer is needed to effect any large scale change or innovation in Biological systems’. So what then is YOUR I.D. hypothesis?
If all it is is that there are things that are designed by intelligent agents and that we can detect such, well then of course that is completely Scientifically valid as long as you are not delving off into supernatural agency.