Yes. Follow these steps to add or change commissioners:
Log into your pool
Go to Commissioner Console --> Member Management.
Find the member you want to be an commissioner and click their row.
On the edit popup, check the checkbox next to Commissioner.
The same steps can be taken to remove a Commissioner if there are already multiple commissioners, however, you can not remove yourself. If you no longer want to be a commish, a secondary commish would need to remove you.
NOTE: The new commissioner has FULL permissions to perform any of the admin functions you can perform. Do not add commissioners unless you are absolutely sure you want to give them these abilities.