{T}: Add {C}.
{2}, {T}: Target legendary creature becomes a God in addition to its other types. Put a +1/+1 counter on it.
{4}, {T}, Sacrifice Tyrite Sanctum: Put an indestructible counter on target God.
An indestructible counter on a permanent gives that permanent indestructible.
You can activate the middle ability targeting a legendary creature that's already a God. You'll put a +1/+1 counter on it.