This is from NFPA 99 2018 / But also is in 2015 & 2012:

5.1.3.5.12.5

The manifolds in this category shall include an automatic means of alternating the two headers to accomplish the following in normal operation:
(1) One header is the primary and the other is the secondary, with either being capable of either role.
(2) When the primary header is supplying the system, the secondary header is prevented from supplying the system.

(3) When the primary header is depleted, the secondary
header automatically begins to supply the system.

? Does this mean, that the manifold shall automatically switch back after the  cylinder exchange or can the manifold be switched back by seim automatic means ? ( i.e. by handle or knob )