Sure it would, add ammonia and ammonia will go up and it should test so.
After a cycle things become more balanced, the bacterias are now in place for ammonia to be broken down into the nitrItes, and the bacterias are in place to break down the nitrItes into nitrAtes. Adding more ammonia will only cause a spike in the system, a deadly spike, which will get converted again as above.
Many things can spike ammonia, feeding, adding fish, some type of death in the tank etc.. but with those bacteria's in place and adding fish slowly over time the system should be able to handle it.