It is stock class legal to have anyone you want install the Toyota LSD. It is not stock class legal, however, to have the LSD but no TC installed. Yes, it's a PITA; the button must be held for like 4 seconds to deactivate everytime you start the car, but the slightest brush by your knee will re-activate it. Some people address this by finding a seat adjustment that keeps their knee out of range of the button, others (like me) use a clear plastic bottle cap taped over the button with clear tape, so you can visually verify the light is on, indicating the TC is disabled.
2005 LRG Elise Sport Pack