The ability only applies while this card is on the battlefield.
Abilities that Slivers grant, as well as power/toughness boosts, are cumulative. However, for some abilities, like flying, having more than one instance of the ability doesn't provide any additional benefit.
If the creature type of a Sliver changes so it's no longer a Sliver, it will no longer be affected by its own ability. Its ability will continue to affect other Sliver creatures.
Standard: Ej legal
Pioneer: Ej legal
Modern: Ej legal
EDH / Commander: Restricted
Pauper: Ej legal
Brawl: Ej legal
93/94: Ej legal
Crystalline Sliver är Legal i dessa block: Rath Cycle