You can use request parameters from json by executing you REST Service from code:
preservice_name.execute({
success: function( PlainObject data, String textStatus, jqXHR jqXHR ) {
//Success handler here
},
error: function( jqXHR jqXHR, String textStatus, String errorThrown ) {
//Error handler here
},
complete: function( jqXHR jqXHR, String textStatus ) {
//Complete handler here
},
data: { object with request params },
headers: { object with request header params }
});/pre
You can replace any parameter and handler to yours. (They are not required)
Thus you can control request at runtime.