You could, but why? If thats what you have, test is test the esters are just different. You might run the cyp first at double the dose for five weeks (inject every 4days) and then the eth for 5 weeks (once a week). This will allow your injection periods to work with the esters a little better. There's no real benefit to the combo, but if thats what you have it will work. Some prefer switching compounds anyway, but test is test IMO.