Can I switch in a new storage drive without again downloading the Mountain Lion installer?

• Buy an enclosure kit from OWC or another vendor.

• Buy and put your SSD in the enclosure.

• Connect SSD/enclosure to your computer.

• Format the SSD with Apple's Disk Utility.

• Use SuperDuper! to copy your entire internal HD onto the SSD.

• Set startup to the SSD and boot from it to make sure it boots.

• Remove SSD from enclosure and install in MacBook Pro.

• Put MacBook Pro's internal hard disk in now empty enclosure and use it as a backup.

You also can use Disk Utility to image the drive if you don't want to use a third party product like SuperDuper! or CarbonCopyCloner. Some people also prefer a simple USB to SATA connector and you can usually get them for less than $5 from Amazon if you don't need or want a drive enclosure for your old drive.

However, the use of your old hard disk in an enclosure and a backup tool like SuperDuper! or CCC gives you both an external drive and the beginning of a solid backup solution as well.

Using a USB Enclosure

If you have a USB enclosure that you can put either the SSD or internal drive in, you can clone your internal to your SSD directly. It's a bit more efficient than pulling from the Time Machine backup. For full instructions, read this, but the short version is:

1. Open Disk Utility
2. Select your internal drive and click the restore tab.
3. Set your internal as the source, and the SSD as the destination, then click the restore button.

Using USB Key & Time Machine

If you don't have access to a USB enclosure (although I recommend getting one — they can be had for $30 or less and are very handy to have around), then you can restore from the Time Machine by creating a Recovery Disk on your USB key.

1. Download the OS X Recovery Disk Assistant, and follow the instructions to create a recovery partition on your USB key.
2. Restart your Mac with the recovery key and Time Machine drive attached, with the SSD installed.
3. Hold down option while restarting your Mac, and select the recovery partition as your boot drive.
4. Choose the restore from Time Machine option, and follow the directions. Select your Time Machine drive as the source, and your SSD as the destination.