Well at this point in the book, Huck is pretending to be Tom so he is understandably nervous when Tom really does arrive. He explains the situation to Tom and he agrees to the plan to steal Jim. This leads to feelings of disappointment in Tom that he would agree to such a thing.
During some of the complicated plans that Tom hatches to free Jim, Huck begins to lose some respect for him. Huck looks up Tom but is also a very practical person and can see that some of Tom's plans don't make much sense and actually put Jim in danger.
Huck changes because he begins to go by Tom's plans rather than making his own. This directly affects the freedom of Jim. Huck wants to just go in and bust him out and get out of there. Tom has an elaborate and unnecessary plan to free Jim. Huck goes along with the plan even though it is cruel to Jim. Throughout the book, we see Huck knows what is right and wrong and he begins to make right choices but when Tom comes on the scene, Huck just goes along with whatever Tom says.