What is the meaning of "Yamreh"?
Rashi: [He will] contest [with your words].
Malbim: Yamreh is actively doing unlike you command. Lo Yishma is (passively) not doing what you command.
If one rebels against Yehoshua, why is he Chayav Misah?
Malbim: He is like one who rebels against the king.
What does "Kol Asher Tetzavenu" include?
Malbim: Even for a minor matter, [if one does not obey,] he is Chayav Misah.
Why does it say "Rak"?
Radak (from Sanhedrin 49a): We accept [to do whatever you command] but not if it is an Aveirah.
Malbim: It is only if you strengthen yourself like is proper for the leader of the nation.