Aye, non of the CLI options are available for the trial. You can contact us about an evaluation version: firstname.lastname@example.org
In the full version (ESS or PRO) you can unpack via the CLI:
Command line interface - Spine User Guide: Unpack
There is currently not a way to use
Unpremultiply alpha from the CLI, sorry. In newer versions of Spine the atlas contains
pma: true when PMA is enabled. We'll have CLI texture unpacking perform un-PMA when that is present, starting in version 4.1.26-beta.
Note we provide our texture unpacker as FOSS, as part of libgdx:
If you wanted to use that, since you have the source, you could customize it as you like.
There is also a libgdx TexturePacker, though it lacks some important features that Spine's packer has (no polygon packing, doesn't know about meshes, etc).