I've been able to create custom Result Source for SP13 people search like this:
var fedManager = new FederationManager(application);
var owner = new SearchObjectOwner(SearchObjectLevel.SPSite, site.RootWeb);
var peopleSource = fedManager.GetSourceByName(Consts.ResultSources.PeopleSource, owner);
QueryTransformProperties queryProperties = new QueryTransformProperties();
SortCollection sortCollection = new SortCollection();
sortCollection.Add("PreferredName", SortDirection.Ascending);
queryProperties["SortList"] = sortCollection;
var currentResultSource = fedManager.CreateSource(owner);
currentResultSource.Name = sourceName;
currentResultSource.ProviderId = fedManager.ListProviders()["Local SharePoint Provider"].Id;
currentResultSource.CreateQueryTransform(queryProperties, "{?{searchTerms} ContentClass=urn:content-class:SPSPeople}");
currentResultSource.Commit();
This works just fine but I still have to manually set "People Search Results" instead of default "SharePoint Search Results" in Type section. Can I do it programmatically? Thank you.