RHQ sends JSON like this to change e.g. the max-pool-size setting of a data source:

{"operation":"composite","steps":[{"operation":"write-attribute","address":[

{"subsystem":"datasources"}

,

{"data-source":"ExampleDS"}

],"name":"max-pool-size","value":75},{"operation":"write-attribute","address":[

{"subsystem":"datasources"}

,

{"data-source":"ExampleDS"}

],"name":"use-fast-fail","value":false}],"address":[]}

Server returns success.
When I directly go to the cli afterwards I see:

[standalone@localhost:9999 /] /subsystem=datasources/data-source=ExampleDS:read-attribute(name=max-pool-size)
{
"outcome" => "success",
"result" => big integer 75,
"response-headers" =>

{"process-state" => "restart-required"}

}

Note the "big integer"

[standalone@localhost:9999 /] /:reload

{"outcome" => "success"}

[standalone@localhost:9999 /] /subsystem=datasources/data-source=ExampleDS:read-attribute(name=max-pool-size)
{
"outcome" => "success",
"result" => 75
}
[standalone@localhost:9999 /]

Now the server acts as always.