Hi,
This is possible in V15.
You go to C:\Program Files\3CX Phone System\Bin\nginx\conf\instance1\ and in here you will find the cert files being used, so all you have to do is get your new updated certificate files, rename them to match the existing files in the aforementioned directory, replace them, then restart all 3CX services and the nginx service.
Given that this is already possible, moving this topic out of 'Ideas' and into General for further discussion if needed.