The "iop*" files are free-software licensed as follows:

* iop_hyperref.bst:

This file is derived from the standard LaTeX file 'alpha.bst',
whose licence states:

    "Unlimited copying and redistribution of this file are permitted as long as
    it is unmodified.  Modifications (and redistribution of modified versions)
    are also permitted, but only if the resulting file is renamed to something
    besides btxbst.doc, plain.bst, unsrt.bst, alpha.bst, and abbrv.bst."

Since the file is named differently, it satisfies the condition for modification
and redistribution.

* iopart_footnotes.cls, iopams.sty, iopart10.clo, iopart12.clo

These files have the licence stated in iopart_footnotes.cls, which states
"Licensed under the LPPL: http://www.latex-project.org/lppl.txt",
which appears to refer to which version of the LaTeX Project Public License
is current. The current version is LPPL-1.3c at
https://web.archive.org/web/20211216154113/https://www.latex-project.org/lppl.txt
and the Free Software Foundation classifies LPPL-1.3a as a free licence:
https://www.gnu.org/licenses/license-list.html#LPPL-1.3a .