samatha after vipassana

>Can one correctly practice anapanasati when one is very used to Mahasi vipassana? How? Why? >Can one correctly practice vipassana when one is very used to anapanasati or any other samatha practice? How? Why? >A person who is used to vipassana is supposed to turn off the habit of seeing things as they are? Can vipassana be useful during anapanasati or would it be more of a distraction to onepointed consentration? How? Why?