Can you add text descriptions to numeric error codes for software installations that will display in Altiris?
Yes.
Can you tell a software resource's command line that certain non-zero codes are still successes?
Yes. For each command line defined for a particular software resource, you can tell Altiris to interpret a non-zero code as a success. For example, maybe for an Office install a success code is either 0 or 3010 (a reboot is required to complete the installation). Enter 0,3010 and it will view both as successful. This is only if you use the command line to call the software resource.
Do the settings at Software Catalog and Software Library > Installation Error Code Descriptions have an impact on success/failure logic?
No. The descriptions only add some helpful information to the codes; it doesn't change how Altiris interprets the codes.
If you want to use a Run Script task that has multiple codes and you want those codes to inform the next task, you need to use Conditions within a Client Job. So you add a Task to a job, and then you add a Condition that says Where 'Dan's Script - Return Value' 'equals' '10002', then run this task and then end. Otherwise, check this condition: if 'Dan's Script - Return Value' 'equals' 10001,' then run this task and then check this other condition, and so forth.
I don't recall if these still show as failures, but the conditions will properly use the return codes to advance your logic.
Does this make sense?