Existing text tags are always rewritten in their original form (compressed zTXt, uncompressed tEXt or international iTXt), so pre-existing compressed information can only be modified if Compress::Zlib is available.
Newly created textual information is written in uncompressed tEXt form by default, or as compressed zTXt if the Compress option is used and Compress::Zlib is available (but only if the resulting compressed data is smaller than the original text, which isn't always the case for short text strings).
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.