Once again, I am stealing from Laraine's topics, but I've been thinking about this question a lot. I do think he changes, but I am not sure of the why.

If you look at the events leading up to his banishment, they end in a rush of passion that kills Polonius. This is the first character that Hamlet kills. Perhaps he sees that it isn't so hard after all?

On his way to the boat with R&G, he encounters Fortinbras army which sets his resolve and, I think, inspires him to act on his honor.

On the trip to England, after spending so much time thinking and re-thinking every issue in order to get it right, one act of rashness saves his life.

Rashly,
And praised be rashness for it, let us know,
Our indiscretion sometimes serves us well,
When our deep plots do pall: and that should teach us
There's a divinity that shapes our ends,
Rough-hew them how we will,

He steals the letter carried by R&G commanding his death and changes it, sending them to theirs. This one act of rashness, or passion, saves his life. Maybe he realizes that acting on your passions can sometimes be benificial? That every issues need not be thought to death? Maybe he also realizes that it is every man for himself?

Then he escapes with the pirates who treat him like thieves of mercy: but they knew what they did; I am to do a good turn for them. Tit for tat, certainly, but more human compassion than he's had in a long time. And from people that are supposed to be worse human beings than the court of Denmark. I wonder if this helps him reaffirm some sort of belief in mankind?

In addition, it seems to me that a little distance from the whole thing calms him a bit. The events leading up to his departure plus what happens to him durning the trip, set his resolve and make issues clearer to him.