Anyone know if Burrrn can add ISRC Codes? If not, would be interested in any other pared down CD burning software that can.
Burrrn doesn't have that feature. Here's a search for ISRC Codes Mastering. Note your burner drive will actually have to support writing them.
The only freeware I've seen that mentions them is in Exact Audio Copy ("EAC") located in 'Tools->Write CD-R', then in CD Layout Editor click 'Options'.
Note: If you try out Exact Audio Copy ("EAC") there's a clean version "EAC 0.99 PreBeta5" without any adware setting off antivirus/antimalware alerts, it's a ZIP archive located here - and yes the download site is trusted, I've used it for years!