Many folks in yoga, do something similar! I have seen quite a few people claiming practice of some poses changes ones mental character and makes one sattvic! The reason given is that these poses acts on nadis (nerve centres) and hence the change! The same problem similar to allopathy. It could be true that characteristics may be possibly totally reduced to the state of the nadis (in the sense that the reason why Russia and US decided not to go for real war during cold war rests on the state of few atoms in the brains of their presidents). But, its next to impossible to put up a constructionist argument for that and hence the claim is silly.
In my opinion, characteristics change primarily only due to effort of the individual. Asanas and other yogic techniques might assist, no doubt, and nadis may probably be involved in that! But, the primary effort is from the individual. To claim that it can be simply achieved by doing some poses is ridiculous!