Slight addendum to Walter's response. For sealed management packs, you are not able to change the Run As profile that the workflows in the MP are associated with.
The BizTalk MP does however ship with two Run As profiles (detailed at
http://technet.microsoft.com/en-us/library/cc655698.aspx). One profile controls the credentials that are used for all discovery workflows and the other profile controls the credentials used for monitoring workflows.
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