Should `CMA_cmean` become a versatile option?

After

```python
import cma
es = cma.CMAEvolutionStrategy(...)
```
the value of the `CMA_cmean` option is available via ``es.opts['CMA_cmean']`` or ``es.sp.cmean``. Do we have a use case where we would want to change the value dynamically via the `cma_signals.in` file?