Modifying Standard OWL

Dear Experts,

For a standard OWL like Opportunity OWL , is there a way to

1. Add default values to some search parameters like Category etc to MyActivities (Query Result) ?

2. Can we add new Query results  (like MyOpportunities can I add my custom QueryResult).

I could not find any option in extensibility explorer. Please let me know if there are any workarounds

Thanks & Regards

Raj