Changing default values for options

It would be nice to have a facility to change the default value of an optional argument. E.g., there could be a method `setDefault` with `setDefault(SVD,DivideConquer=>true)` resulting in resetting the default from `false` to `true`.

This would be useful in a scenario when a user

- writes code that relies on popular methods (e.g., `SVD`, `gb`, `res`, etc.) without explicitly referring to strategies, and
- experiments later by tweaking strategies.

No source files, tests, or entry points are named in the issue. Start by locating how optional arguments and strategy defaults are defined, then determine the scope and semantics of a facility that changes defaults; done should include a documented way to override a method's default and coverage for the SVD-style example.

Written by the indexing model from the issue text.