Can I double the dosage on the use of rogaine (minoxidil) once a day so I can style my hair after and not have to wash it twice for a double rogaine (minoxidil) application?

Not really. Applying more Rogaine (minoxidil) on at one sessions not as effective as twice a day treatment. However you don't have to wash your hair twice. Rogaine works on the scalp. Careful application can be made without having to lather it all up in your hair.