Product question regarding U3S/U3B custom code additions


I wish to connect an external DAQ chip and associated circuitry to the U3B's onboard Atmel 328 to perform some operations and measurements the 328's internal ADCs can't do (I'm assuming that the U3B will use the same microcontroller as U3S).  Is there a way to add a piece of user's code that the unit will call periodically?  If yes, is there a way to save some text containing the data such that it can be incorporated into the transmitted message?

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