Forms give us the substance of our art. The answer by most masters is yes, a form may be changed, as long as the change is for the better. Lets say you have difficulty with your front kick. Your instructor adds a few to your form. Now your championship form looks horrible but your kicks will improve.
Forms are the foundation but no two people do a form the same way.
It's all in in terpretation. Forms most often have a theme to them. In my style of Kung Fu, the form Lao Ying tells of all the pressure points on the wood chi channel in the body. I have seen Karate forms that teach how to defend from rear attac ks and Tae Kwon Do forms that show how to fight against someone on horseb ack. Forms can also show what time of the day to use certain techniques.