By all means, state clearly that the interface could change. Given it's the OP's first CPAN module, however, he should certainly seek advice on a proposed interface, and especially on module name, before uploading.

As for actually using the module to determine how good the interface is, that is one of the many benefits of test-driven development: each test is a first class user of the module's interface and the act of writing the tests often causes one to change the interface. An interface that is hard to test is often hard to use. Code that can be unit tested in isolation is well de-coupled. Writing tests early improves design and interface.

The practicality of changing an interface depends on how widely the module is adopted. For example, because File::Find is so heavily used, it has become practically impossible to change its (unfortunate) interface ... well, until Perl 6 rolls out, that is.