Example of injecting parameters

Jenkinsfile

// Import classes 
// To work with hudson.model we need have access to System Groovy
// it can be provided by Groovy plugin
import hudson.model.*
import java.util.Map;

// Create directly object of class CascadeChoiceParameter
// which will be parameter
CascadeChoiceParameter CCPCluster = new CascadeChoiceParameter(
    "ClusterName",
    "ClusterDesc",
    new GroovyScript(
        new SecureGroovyScript(
            "return ['dev', 'stageb']", 
            true, 
            []
        ), 
        new SecureGroovyScript(
            "return ['Error']", 
            true, 
            []
        )  
    ),
    "PT_SINGLE_SELECT",
    "",
    false
)

// Init function for injecting parameters into model
def custom_parameters(Map all_parameters) {
  def new_parameters = new ArrayList<StringParameterValue>();
  new_parameters.add(CCPCluster) 
  return new_parameters;
}

// Init variables needed to inject
// namely get current Thread (need to import hudson.model)
def thr = Thread.currentThread()
def build = thr.executable
def all_parameters = build.getBuildVariables();
def new_parameters = custom_parameters(all_parameters);

// Inject the new parameters into the existing list
def modified_parameters = null
def old_parameters = build.getAction(ParametersAction.class)
if (old_parameters != null) {
  build.actions.remove(old_parameters)
  modified_parameters = old_parameters.createUpdated(new_parameters)
} else {
  modified_parameters = new ParametersAction(new_parameters)
}