I have had several changes of insulins over the last 21 years for verious different reasons...
You've been on the same insulin for a long time, and it's gone through many different changes and phases of your life... As you know you are a lot different person now from when you were 9 years old...
It could be that the reaction of the insulin no longer matches the interaction of your body workings or currant lifestyle and anopther insulin which slightly different properties and interaction might suit you better...
Not sure whether I would class this as the body resisting your insulin, more a case of the insulin not being in tune with the body...
But it would be well worth talking about this with your diabetic team,
When you do I would...
Before hand take a look at your BG reading, note down why you feel that your insulin isn't matching you any longer... Link this up with your readings, and activites sorrounding these reading the better and more indepth peicture you can build around showing your control, the more they will be able to help you..
And what you want out of your insulin so that it enables better control..