There should be a way to make the invite list for a conference editable even after it has concluded in the default version of Canvas Conferences. Once a conference has concluded, there is not a way to change the invite list for the conference. See this question: Adding students to a Concluded Conference? for information on this problem from the product manager for BigBlueButton.
Here's the use case that prompted this feature idea: I have an online instructor who does weekly lectures using Confnreces. She had a student add to her course late. Since this student was not in the course when the conference was created, she was not on the invite list. Sadly, however, we learned from looking at the above question that not only can the list not be edited, the link generated isn't shareable. So, even though the recording had not expired, it was still useless for this student.
For cases like this, and the others referenced in the answer to the linked question, this is a feature Canvas should consider.