I've replaced the RAM, wlan card and both hard drives in my 2013 Blade Pro. I used an MSata Crucial 480gb in place of the stock MSata cache drive, and a Seagate 750gb hybrid hard drive in place of the stock 500gb drive. The Seagate is slightly thicker than the stock drive - I had to leave off one of the HD bumpers. It fits so snug without it that I think it's safe. Both drives are accessible with Windows 7 - I use the MSata as a boot drive and the Seagate for media. It wasn't too hard to do, just go slow and keep track of what screw goes where.
Razer had the battery made just for the Blade, and they absolutely refuse to sell them. The warranty on the battery is only one year, and is not covered by an extended warranty. Once the battery goes, that's it - you now have a desktop computer. I've gone round and round with Razer on this issue. The only option is to take apart the stock battery and hope that you can find the cells they used to make it.