Spark - user register with existing team

I am playing around with Spark for the first time, and it would appear that unless you are invited to join a team there isn't a method to register to an exiting team. Is this the case? Anyone develop a work around?

Ideally I am looking to use Teams as a company so that users have to register as belonging to a company. There should be two processes one which a user self registers and waits for approval and another where they get invited. Spark has the second functionality built in but I am looking to add the self register and approval process. I don't want to break the existing invite process so I am assuming that I am going to need to develop a new User registration process and use the existing "Register" process for companies only.

In general, if I change any of the code in the Spark folder (not including views) I am assuming it would likely be changed back on future updates. There is quite a bit of functionality that I am going to need to change... for example I want users and teams to be able to store multiple profile images. I notice right now when you add a new photo it keeps adding an image into the image folder but the user cannot access the old ones. I can see this folder becoming full of useless images.

While I appreciate the work that has gone into Spark, I think that I am likely going to be modifying it so much that all future updates wouldn't be of any value to me. I guess I could cherry pick files from updates, but that could get problematic.

Curious as to how everyone else plans on using Spark. Clay