I understand the importance not to flip cards during the match, but is the content of your own deck before the match has started really be considered hidden information to you?
Technically, pregame sideboarding and shuffling are 2 distinct steps in the pregame procedures, but they can be repeated. Presumably while in the act of sideboarding it's not hidden to you, and when shuffling it is (since you shouldn't know the card faces of randomized cards). I would be careful about intentionally revealing randomized cards in a deck while actually shuffling, since this same act (while it could be done to trick an opponent) also facilitates you cheating by actively attempting to gain hidden information (the identity of a randomized card in the deck). However, there is nothing preventing you from executing any number of the following steps:
1) putting or "dropping" a card face up on the table while sideboarding
2) placing that card on top of your deck
4) stop shuffling, and begin sideboarding again.
5) shuffle again
If you wanted to do it before the match starts before game 1, I think you'd again be ok, if you "dropped" something while looking through your deck before shuffling, but tracking a card while you're actually shuffling for pregame procedures in order to intentionally drop it is probably not a good idea.
To put it simply: if a judge sees you do this when you are allowed to be looking at your deck, you're ok...if a judge sees you shuffling and it is obvious to him that you are tracking a card or trying to glimpse what a particular card is while shuffling it's not ok, even if you use the excuse "I wanted to intentionally drop it".