Thanks for showing me the link to the non-roster invitees. I see it now. Sometime in the past, maybe last season, the drop down from the top had a link to the non-roster list, but I see now that it is on the page of the 40 man roster.
From what I have read, the 60 man list is due to be set this weekend and changes after will involve normal player moves such as direct assignment, waivers, or release to free up space to add someone else. I think I read somewhere that they cannot add anyone from within the organization to the 60 after the list is set, but that doesn't sound right. Of course, if a player is not on a 60 list with some club, they probably would require a couple weeks of isolation and work outs before being allowed to join a club.
There is also the Nashville plan which MLB is working on. This would be a group of 60 or so free agent players working out and playing games against each other at the Souinds' facility in Nashville. Teams could sign players from this group as needed during the 60 game season.
Still much to learn about how it will actually play out.