I would like to add memory to my MBP, but I am worried that if I do this myself I will be in jeopardy of voiding my warranty. Is there an authorized way to have memory added that will not void my warranty?
No - a simple and properly done RAM replacement does not affect warranty coverage. You can have Apple do the work, or an authorized service provider to do the work or hire someone. Just understand what is covered if something happens before you pay for service.
When someone breaks a mac when it's used in a way not intended, that can result in a denial of warranty service. Also - using aftermarket parts that then damage your mac can also land you in hot water. Luckily with RAM, as long as you don't physically break the mounting brackets, usually the worst thing that happens is your mac is unreliable or panics until you get proper RAM.
The user manual for each Apple product will clearly explain which parts are user replaceable and which are not. You can look up your manual online if you care, but no portable machine other than the MacBook Air has ram that is not user-replaceable.
The best way to answer this kind of question is to check the Apple manuals and documentation that came with your computer. For example, the current generation MacBook Pro 15" User Guide has a section for "Installing Additional Memory." That means that Apple considers installing RAM and other things noted in the manual as user replaceable parts. So as long as you follow all the installation and safety instructions listed in the manual you will not void the warranty for properly installing user serviceable parts.
Additionally there is another authorized way to perform the memory upgrade and that is to take you computer to Apple or an Apple Authorized Service provider and allow them to do the task for you.