Re: cherry-picking poskim, a well-known Gemara (Avoda Zara 7a) states that once one halachic authority is questioned and rules regarding the halachic status of an item, no other authority should be questioned to procure a differing ruling:
[1]
[2] With the exception of where a mistake has been made by the Rav, in which case the initial ruling had no potency. See the Ritva there and the Rema and Shach (cited below), for a discussion of which mistakes this is true for.)
One final caveat. The whole discussion here about the essence and power of psak only holds true to a ruling made on a specific item: e.g. the Rav is consulted about the kashrus of the chicken; or the beracha on a food, however, regarding a general halachic enquiry: for example, what is the halacha if I forget ???? ???? on Rosh Chodesh, should I follow a certain practice or minhag, the above discussion is not relevant. In such a situation there is no physical item for a ???? of psak to become active (Chut Shani, Y.D. 188). It is to be explained how it is in such questions that a ruling can obligate the ???? to follow the words of the Rabbi.
(above from A Prager)