AID is used to uniquely identify your application on the card. It has two components:
RID is issued by ISO and the companies need to obtain a unique RID from ISO. RID should have length of 5-bytes while PIX is propriety to every companies and it is also an optional part of the AID. It's length various from 0-11bytes. Now if you are using AID for learning purpose than you don;t need to have RID assigned by ISO, you can use any (hex) value within range of 5-16 bytes as your applet'/package' AID.
I wonder, because the system is used for in-house book-keeping purposes. It has nothing to do with the outside world. Is it safe to ignore any iso assigned id, and continuously use the casual 'id' that I give to it?