You don't have to physically take the button out to replace the LED. The power LED pulls easily out of the holder it's in - there's just a tiny bit of hot glue holding it in.
I've replaced the blue LED on my Define Mini and Define XL with green ones, and glued a red LED to the side of the clear plastic surround to act as a HDD LED. Works perfectly - the plastic glows green and when the HDD is accessed it flashes red. I just hot-glued the red LED to the side of the clear plastic, beside the green one.
Both LEDs are normal 3mm items.
Workstation: Dell Latitude E7440, i5, 1080p screen, Crucial 8GB, Crucial M500 480GB mSATA, Win7
NAS&Downloader: XPEnology PC, AMD E2-2000, 4GB, 2x Seagate 4TB ST4000DM000, 2x HGST NAS 4TB, DSM 5.0
HTPC1: TranquilPC ABEL H2, i3, 4GB DDR3L-12800, Crucial M4 128GB mSATA, Win7
HTPC2: Akasa Euler, DH61AG, Pentium G620, 4GB DDR3L-10666, Crucial M4 64GB mSATA, Win7