You can change your old blogger login email to new email id..
If you want to use a different email address, whether gmail or other email address, to access Blogger, all you have to do is to

sign into Dashboard and
and add yourself with the new email address as an author.

A invitation would be arrived in your new email address.Better open it in new browser and accept this.
Now go back to your Blogger account in the other browser where you are still logged in and in the PERMISSION tab. You should see your other email address added as an author. Give yourself admin rights. Now if you are sure that you have added yourself with the new email address, you may remove yourself with the old email address if you wish.
Now onwards you can use the new gmail address to Login the Blogger.