As of right now, no there is not a way to rearrange the order of accounts on the bottom of the side bar, so the Microsoft account would take precedence. However, any email after that, one can rearrange that order, if they change the settings of the accounts so they are in such an order, or add them sequentially as one intended.
This is done in the Charms settings when you have the Mail app active under accounts.
Possibly not the ideal way, but one can always still submit feedback on a feature to add.