We would like to user the service desk to allow customers to create bugs and feature requests through a simple interface on an existing Jira project.
There would then be 'agents' that would curate these issues and then hand them to the development team if confirmed.
This all works nicely and as expected. The only problem is that the developers are not 'agents' but 'collaborators', and Service Desk therefore prevents them from editing / transitioning the issues.

It means we cannot streamline our support with our development process. We would need separate support and development projects and duplicate/link the issues between them.

Would it not be possible to remove this restriction? The collaborators should be able to do whatever their given permissions are. They don't need access to the full service desk view. We are still paying for their user license anyway.
Agent licenses will still be needed (and purchased) to use the full Service Desk portal features. Otherwise it is a convoluted user experience.