14mm axle, 10mm drop outs?

Ive got a new Rear wheel with 9tooth for my BMX and it has a 14mm axle. My frame has 10mm drop outs, should i Slot the Axle on the drop out part to 10mm or File the drop outs to 14mm. I have a spare frame to practice on. Also if i did Slot the axle on just the dropout part to 10mm and then i get a new frame later with 14mm dropout will it still fit okay?