Add 4096 length DKIM keys?

Hi Everyone, Just wondering is there any way to add my own DKIM Private/Public key to exim server in Cpane/WHM without have been worrying about losing data with next update? Currently Cpanel/WHM Generate its own DKIM with Default key! its ok but I want to use 4096 length for my keys! cause at the moment everything with my DKIM is ok but DKIM Authentication, MXtoolbox just shown me something like this: DKIM-Signature Not Verified! maybe using external services like unlockinbox can help! Don't know :( Thanks a lot and have a lovley day :)