I've got 29 otherwise identical MicroTrains NKP hoppers in 6 numbers. I've considered renumbering 23 of them, but piecing together 5 digit car numbers from number jumbles 92 times isn't my idea of fun (4 numbers per car). Plus I haven't yet found the right size numbers that matches what's on the car The only "good" news is that these cars are old enough that there are no numbers or reporting marks printed on the car ends, so at least I don't need to remove or match them. So for now, I'm leaving them alone.
On the other hand, I have 6 other MT notched-arch-end hoppers all numbered NKP 33799 that WILL get renumbered. Luckily, K4s has a decal set for these, and it just happens to come with 6 numbers! This will get done by painting over the existing reporting marks and numbers, then applying the decals. i did an experiment and it it works nicely.