G2S: How much can I change after purchase?

Hey all,
I recently bought an Asus G2S-A1 through a guy that I know personally in order to get a $600 discount. I am very happy about my order and the price that I got from him. However, he told me that the only way I could get the discount was if I bought the notebook at stock. I wasn't really that bummed out about it because the price was pretty amazing to me and he told me that he could upgrade the memory for me afterwards anyway, so that was good. I had also wanted to upgrade the proccessor but im pretty sure I cant do that anymore, correct? Also, I wanted to upgrade the 160GB 5400RPM harddrive to a 160GB 7200RPM harddrive.

First, is it even worth worrying about the 7200RPM I wasn't able to get?
And second, if it is worth it, is it possible to switch the hard drives out?

Thanks!

Edit: Oh, and are there any other upgrades worth worrying about? Or is this notebook pretty good as is?

 

7200rpm HD's aren't as good of a purchase nowadays unless you need every second(encoder, etc.). 5400rpm HDs are very comparable in speeds due to the larger disc trays and cache, and you can get a much larger sized one in comparison to a 7200rpm HD.

And yea, the HD can be easily replaced.

 

The T7500 it comes with is a little over the price-poerformance sweet spot. The only CPU better than it that'd work is the T7700, which is way not worth it.

 

ok, thanks guys.