The Artistic License 2.0 (and possibly 1.0/1.1; I'm not as familiar with their license texts) specifies making changes available to the original author (without necessarily making them public) under the terms of the original license as one option for conditions by which one can use Artistically Licensed code (along with "give it a new name and don't interfere with installing the original version" and "release the source code publicly under a FOSS license", in that order).