If there's a reason to store something in the system DB's - I'd put it in master (it's a reasonably common practice). Is there a specific reason you want to put it in MSDB? Like Vyas pointed out - MSDB is one of the files where all sorts of processing occurs, and I wouldn't modify it at all unless there's a darn good reason to do so.
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Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?