GetComponent(TextMesh).characterSize = 10;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Awake() {
GetComponent<TextMesh>().characterSize = 10;
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Awake():
GetComponent[of TextMesh]().characterSize = 10