Add note about changing JobAcctGatherType in slurm.conf

doc/man/man5/slurm.conf.5

@@ -787,6 +787,12 @@ cgroup cpuacct subsystem: user cpu time and system cpu time. No value
 is provided by cgroups for virtual memory size ('vsize').
 In order to use the \fBsstat\fR tool, "jobacct_gather/aix", "jobacct_gather/linux",
 or "jobacct_gather/cgroup" must be configured.
+.br
+\fBNOTE:\fR Changing this configuration parameter changes the contents of 
+the messages between Slurm daemons. Any previously running job steps are
+managed by a slurmstepd daemon that will persist through the lifetime of
+that job step and not change it's communication prototol. Only change this
+configuration parameter when there are no running job steps.
 
 .TP
 \fBJobAcctGatherFrequency\fR