C# What pattern to use to be more flexible

I am building an interface to read, validate, convert and store data. In this way two systems can cummunicate with each other.

I have created a generic flow which works fine and is very extensible:

IProcessor< P, S> -> Proces() : void

IProvider -> GetItems() : IEnumerable< string>

IValidator -> Validate(string) : void

IParser< P > -> Parse(string) : P

IMapper< P, S> -> Map(P) : S

IStorage< S> -> Save(S)

new Processor(IProvider, IValidator, IParser< P>, IMapper< P, S>, IStorage< S>)

The problem is that there is a business rule which states that P must be mapped to S1 or S2 depending on a Value. How to alter the structure, so that it is more flexible?

Thanks,

Najra