I never found that to be a problem, as I always did my Tresiba at breakfast, so it was a dose of Novarapid, and a dose of Tresiba. Just getting into the routine, and avoided the problem of forgetting, or taking the wrong one, at bedtime. As
@helli said, you couldn't change the dose easily, but I found that having the longer acting (42 hours) of basal, and having it at breakfast, it meant that I had effectively a reduced dose overnight as the first overlapping dose phased out, but maintained a steady basal during the day. Any adjustments were done with reducing or increasing the bolus.