Foolestroupe,
Since I came to the concertina from P/A too I easily assimilate what you are saying and starting from the end I do agree that these methods for articulation can be practised with concertinas also.It is more difficult with the concertinas due to their floppier bellows (except old treble englishes with 4 folded bellows)since you can not get the same support and stability neither of the bellows itself nor from the weight/inertia of the instrument.Even resting the concertina on the knee does not offer comparable stability."Give me a stable point and I move the Earth" - is that what Aristoteles said...

On the other hand the lighter concertinas offer other means for similar srticulation and your latest tremolo example is one of them.
Just fluttering/flickering (? I don't know the best word in english) one or two fingers in the air, or delicately tapping the end plate can produce some minor tremolo too.

What you describe actually resembles how "bellows shake" is sometimes explained in accordion tutors (most tutor authors try some variant of their own to explain these subtilities in a more or less in-comprehensible way).

One specific articulation issue is trying to simulate violin "vibrato" which technically is impossible with squeezeboxes since the pitch can not be altered regularly with them - we always end up with some kind of *tremolo* (variating amplitude).Since the single-reeded concertina tone is dry in itself we don't have the options to "wet" the tone by using double reeds ( or 3 with "musette") as with accordions.To do that one can use some of these methods you speak of too - do you have any particular view on that?

At last one little remark. No question "inertia" related to the weight plays some part in all our activities but when talking about the effort of bellowsing we can separate some movements for which the weight is important and some for which it is not.For doing many of these articulation "specialities" weight has influence, but for simple "pumping" itself (as when moving the bellows in and out in a straight line) it is the cross-section of the bellows that causes the difference in effort ( and air flow resistance over the reed slot of course, and also the effort carrying the instrument but that strictly speaking is not necessary for sound-making)