Is it ok to swap my Mac's HDD?

I have a Seagate ST9500423AS 500 GB lying around which I believe is 7200 RPM (correct me if I'm wrong)

Is it possible to easily swap it with the preinstalled HDD that came with my MacBook Pro? Would that void my warranty?

Also, when I install it in my MacBook Pro, will turning on the notebook while holding the Command + R key work to enable me to install my Lion OS again?

Is that recovery thing built into the BIOS of the Mac or is it lying somewhere on my current HDD?

Please advice with the steps involved if this doesn't void my warranty and is fairly easy to do

 

As long as you have the right tools, swapping a drive in a unibody MacBook Pro is easy and will not void your warranty. There's a really nice guide, with step-by-step instructions, with detailed photos, here.

It even tells you what tools you need, and you can buy them from that site. The spudger (used to disconnect the battery) isn't entirely necessary as I've swapped my hard drive out several times without it. You just need to exercise caution.

If you're going to swap the hard drive, while the case is open, you can take the opportunity to upgrade your RAM as well. Any 8 or 16 GB kit (2x4 GB or 2x8 GB) of DDR3-1333 or DDR3-1600 should work. Brand doesn't matter. Buy whatever is cheap. The guide for doing this is here.

The links I've provided are for the early 2011 MacBook Pro, but your is, functionally, no different.

Yes, just make sure you have an Internet connection when doing so as the installer will need to download all the necessary installation files.

There's a small recovery partition that's created, but again, much of the reinstall happens through downloading.

 

Thanks for the detailed info