I don't think so. I think the only thing requiring the AMA number on or in the airplane is the safety code, and it is not specified that it has to be displayed anywhere. The individual event rules define whether or not it has to be displayed and how. If the individual event doesn't require it, a slip of paper in the tank compartment with the AMA number on it will suffice.
Brett
Actually, Brett, it is in the General Rules. It says something like
4. Identification: All models, except Indoor,
will be identified with the owner‟s name and
address or AMA number, on or in the model.
Individual events listed within this (Competition
Regulations) may have additional identification
requirements which must be adhered to.
"Additional" e.g. the minimum size and placement for stunt