On my Mac, I have installed the required certificates and keys to develop and distribute my own personally developed iOS Apps via my own iOS Developers' License. However, my client would like me to use his License to distribute (Ad-Hoc) betas and eventually distribute the app to the app store.
Please can you tell me how I can install his developer license on my Mac without affecting my personal developer certificates and keys already installed on my Mac?
Furthermore, is this even possible?
Edit---
Sorry, I didn't mention; I don't want to have to revoke my client's pre-existing certificates on his developer account.
Contrary to one of the comments, you can't download the keys from Apple - they only exist on his computer. It is only the provisioning profiles that you can download from Apple. So if you don't want to have to revoke his existing distribution keys, he will need to export them from his computer.
He can do this by going into the Keychain Access -> My Certificates and looking for the entry called "iPhone Distribution: My Company Name". Then right-click on it and choose "Export ...".
He can then send you that file, which you can double-click to import into your own Keychain.
And it is fine to have multiple keys on your computer - it shouldn't affect your personal account.