import com.atlassian.jira.ComponentManager;
import com.atlassian.jira.issue.fields.FieldManager;
import com.atlassian.jira.issue.fields.CustomField;
import com.atlassian.jira.issue.fields.layout.field.FieldLayoutManager;
import com.atlassian.jira.issue.fields.layout.field.FieldLayoutItem;
import com.atlassian.jira.issue.fields.layout.field.EditableFieldLayout;

//*** Initialize Output ***
String result = "";

//*** Get Needed Managers ***
ComponentManager   componentManager = ComponentManager.getInstance();
FieldLayoutManager layoutManager    = componentManager.getFieldLayoutManager();
FieldManager       fieldManager     = componentManager.getFieldManager();

//*** Lookup Field Layout ***
EditableFieldLayout layout = layoutManager.getEditableFieldLayout(10000);
log.debug(layout)

//*** Lookup Custom Field ***
CustomField     field = fieldManager.getCustomField('customfield_10042');
FieldLayoutItem item  = layout.getFieldLayoutItem(field);

log.debug(item)


//*** Record Old Description
result += "Old Description:\n----------------\n"
result += item.getFieldDescription();
result += "\n\n";


//*** Update Field Description ***
layout.setDescription(item,"SSSSew Field Description");
layoutManager.storeEditableFieldLayout(layout)


//*** Record New Description ***
result += "SSSNew Description:\n----------------\n";
result += item.getFieldDescription();
result += "\n\n";

return result;