Is it possible eg for the list-owner to accept postings wihtout going through a browser?

Not to my knowledge, but:

I own a large number of lists, and although I have set open posting I am still asked to verify that I accept postings.

this makes no sense. If the list is "open", no approval is necessary for posting. Perhaps you've got something configured slightly wrongly; check that stuff again.

Basically I would like to be able to write a short Perl script which would say "Yes" to them all.

There are other places too where a text interface might be an advantage.

It's been brought up before.