How else do you deal with all the import invocations in the source code files with outdated versions?

M4? Make + C preprocessor? Perl generating Perl? I tried to guess the least-absurd option for updating a library.

Please inform the rest of us what the standard tooling for handling this in the Perl community is.

Of course. A true Perl user has no need for sed, when there's "perl -pi -e".