What right did Yakov have to use does devious methods for his personal gain?
Ramban #2: It is even possible that Lavan - who knew nothing about the novel method that Yakov would ultimately employ - gave him the green light to use whichever method he saw fit.
Moshav Zekenim #2, Da'as Zekenim, Hadar Zekenim (38), Riva (32): Lavan cheated first. He was supposed to remove only young animals; he removed also adults. 3 The sticks were to compensate for this. "With the crooked 4 , you may be crooked" (Shmuel 2:22:27). 5
Bechor Shor (33): It would be proper to leave the spotted animals in the flock, and the females could see them and give birth to such babies. Due to Lavan's adamancy, lest he claim "these spotted animals were born beforehand", they had to be removed. The sticks were to compensate for this. Yakov stipulated to do so, and he did so openly.
Tosfos ha'Shalem (35:3), Redak (40): Yakov used the sticks only on his own flock (what was born spotted, after they matured), lest they give birth to animals without the Simanim, and they will belong to Lavan. 6
Moshav Zekenim #1, Tosfos ha'Shalem (3): An angel told him to do so 7 , like it says below (31:10-12).
Moshav Zekenim #3: Yakov intended to benefit Lavan 8 ! He prevented his own animals from mating with Lavan's lest the babies look like the fathers. And he covered Lavan's sheep to keep their wool clean. 9
Tosfos ha'Shalem (Perek 40 Pasuk 4): He intended only to help the animals give birth. Refer to 30:42:1:5*.
Ohr Zaru'a (1:769): Yakov used the sticks only on his own flock, and did not face Lavan's flock towards those with the appearances that Yakov receives, lest Lavan say that they give birth to these appearances because they see such animals.
Malbim: Lavan should have left in the flock animals with white, so the female could see this and such animals would be born. Lavan removed everything with white, so the sticks were in place of this (something white for the females to see). 10
Even though he did not cheat, since it looked unjust, Yakov's children and their land were annihilated (Tosfos ha'Shalem 42:1).
Riva: He removed also Akudim, the healthy animals (and everything with white - Tosfos ha'Shalem 2) and the females (Tosfos ha'Shalem 4, citing Chatzi Menasheh, citing Riva of Orleans), and he changed the wages 100 times.
Tosfos ha'Shalem (1): Yakov took Livneh, Luz and Armon, to hint that he does so because Lavan is acting Naluz (crooked) and with Armimus (guile).
Tosfos ha'Shalem (33:5): This Heter is only for the same matter in which the other party cheated.
Riva: We say so to answer heretics; but it is not correct!
Tosfos ha'Shalem: Surely, had the angel not told him to do so, this would have no effect!
Ha'Kalir put "Meyachem b'Maklos b'Shikasos ha'Mayim" in the Piyut "l'Ma'an Tamim..." (the fourth that Ashkenazim say after finishing the Hakafos) on Hoshana Raba. Surely we do not request in the merit of trickery!
Tosfos ha'Shalem (2): Also, he caused Lavan to get animals born in summer, and Yakov got those born in winter.
Ha'Emek Davar: The Petzalos were like spots, and Machshof ha'Lavan was like blotches.
Why does it say that only the Livneh was moist?
Bechor Shor: Livneh is white only when it is moist. The others are white (under the bark) even when they are dry.
What is Luz?
Rashi: It is a tree that makes small nuts.
Riva, Moshav Zekenim: It cannot be a tree that makes small nuts, for Bechoros 8a says that it bears fruits in 21 days! Rather, it is an almond 1 tree.
Riva supports this from a Midrash (and Yerushalmi Ta'anis 4:5), which says that almonds develop in 21 days.