an1285 While it's certainly preferable to use the original Spine project for upgrading Spine skeletons, you can still perform the upgrade even if the original project is unavailable. To do this, import the exported skeleton data (.json or .skel.bytes file) into Spine 3.8, save it as a Spine project, then reopen it in the 4.1 editor and export it again.
As Spinebot answered, all these operations can be performed through the command line interface. We also offer scripts that are easier to use and more adaptable to your needs, so be sure to check them out:
Blog: 새로운 셸 스크립트로 내보내기
