This is a workaround not neccessarily a feature of AltSpace. For some reason in personal homespaces you cannot add builders, pilots, terraformers etc. The permissions wont be granted and it can be frustrating if you have someone who you trust or need help.
By adding the permissions (example) in the default contextual permissions you can assign default permissions to everyone who joins. This is something I only recommend while you are in your room to ensure that nothing happens after you leave and someone enters your space.
Even though the option to add friends is on the page you will get an error when you go to change. This is a workaround working as of 14th April 2021.