No. it will not void your warranty to upgrade your HD to a SSD
However obviously the SSD will not be covered under same and any damage you potentially cause in the install is not covered
Apple instructions themselves indicate user upgradable RAM and HD/SSD
Page 37 manual tells you how to replace a hard drive (which Apple would not tell you to do if it did void the warranty)
There is a specific reference to this in the Warranty text that says it's OK for drives and RAM to be replaced by the user provided they don't damage any components in the process.
"any damage caused while making the update would not be covered with AppleCare extended warranty"
Final determination is up to Apple resultantly if damage is incurred in any way to your upgrade. As such you need to know what you are doing, and be SAFE is doing same.
Ive made countless such upgrades, but most have not and could shock the logic board, or easily cause damage from lack of knowledge.