SQL Server Agent Proxy Password Management

I must be missing something. 

I recently set up a new set of Credential Properties for a domain user account in SQL Server 2014. The Credential Properties only required a name, identity and password for the domain account.

Then I set up a Proxy for SSIS Package Execution using the Credential for this domain account. 

Do I need to manually edit the password every time the password expires? Is there at least some T-SQL script that will allow me to change the password in the Credential store? What am I missing?