Not all actions require administrative privileges on the target machine. For the ones that do, you'll either need to run your browser as a different user or (as you indicated) add runas to your action path under Configuration\Asset Pages. Several customers have requested that we add the ability to run actions under your scanning credentials for instance, but we do not have a release date for this feature at this time.
For some things, like shutting down a computer for instance, you could use a deployment package instead. You can choose which user account (system account, scanning credential, currently logged on user) to run a deployment package under. More info on creating and running packages can be found in
this section of our knowledge base.