No it's not too late, and technically you don't even need to re-install Windows. What you use is "cloning software" which creates an exact copy of your entire existing hard drive on to the new SSD, complete with all data, Windows and activation intact, including all your preferred Windows settings and any third-party applications that are installed on the existing hard drive. In a nutshell, the SSD will be an exact copy of the hard drive.
I use a commercial hard disk copy software, but this free one is very popular:http://www.easeus.com/disk-copy/home-edition/
Needless to say, both drives must be visible to the cloning software, so you'll need to install the SSD either internally as a second drive, or put it into an external hard drive enclosure. Then, when the cloning is done, you swap the drives over so that the SSD then becomes your Windows boot drive.