What are some potential consequences for attempting to cure Type one Diabetes?
High school biology apparently failed to teach you that many conditions, like type I diabetes are not classically Mendelian. The term "carrier" does not apply to you...you are just someone with a predilection who hasn't developed the condition (but who might...I have heard of someone developing type I diabetes in college)


  Scientists develop a modified virus that contains a normal person's
  beta cell genetic makeup,


How much DNA do you think you can cram into a virus?  Not having the right beta cell DNA is almost certainly not the cause of type I diabetes, anyway.


  The virus and beta cells reproduce, and the body detects the virus,
  but not the beta cells.


How do you think the immune system responds when it detects a virus?  Hint, it kills the hosting cell.  

A virus that induced a small percentage of pancreatic alpha cells to undifferentiate and redifferentiate beta cells might work...but you would still have the same immune system that went agro on your beta cells the first time.  They might do the same when exposed to new beta cells.  And there is a fine line between undiffernetiated cells and cancerous cells.