Support for ignore some 'unused' keys

In our project sometimes we need to generate translation keys by concatenating strings.
If we don't use the option 'safeMode', those keys are removed.
The problem is that if we use it, those keys remains untouched but the unused keys (generated by typos or just not used) are not removed.

It would be really nice to have an option to avoid the removal of the 'unused' keys from a specific module, while keeping the behavior for the remaining modules untouched.