immigration at airport ? if it's at the office they can't cancel it as you are automatically without visa and still inside the country . but i have many friend who was on ED visa and jump to non-B and never have problem to change it . but anyway we all got our experiences
in my case no , in the case of some close friends yes . anyway to apply non-b you have to get out right , apply outside Thailand ( i not mean the 1 year renewal but the first 3 month non-B before getting the work permit ) . you fly out stamping you passport out and when you come back just tell immigration you change visa .... but never go to immigration before fly out and ask then to cancel it . does it make sense ?