tape_name is read only via API. Look down at read only properties for PySegment
Hopefully soon we will have full flexibility to add whatever metadata tags we could ever want.
I dont know what you are up to but I cant help myself and say that clobbering the tape metadata might not be the best. I treat tape & timecode metadata to be sacred, then shotname metadata would be present in the folder structure and filename (ex, shot abc0010 would in …/shots/abc0010/plates/…/abc0010_addl_details.####.exr) during publish. Having tape metadata present really helps track down the camera RAW after publishing. If you ever need to extract the shot name back from published plates or shot name was clobbered but you still have segment names, its possible using this method
If you really want to do this, you can manually edit the tape name in the conform tab for the open sequence.