I want to run transmission-daemon as a service so that any user can log in and access the same instance of Transmission (via the browser or Transmission remote GUI).
Is this possible, and how can I do it?
You just install the transmission-daemon
package and it'll be started automatically during boot via the init script it installs. The instance that is started via the init script will be run as the user
See https://trac.transmissionbt.com/wiki/EditConfigFiles on how to edit