Occasionally I will paint up one figure as something else, if the uniform is right.
Here is a picture of the Don-style cossacks (RUC-5) painted as a World War I cossack (left) and as a late 19th-century cossack.
The style of the uniform didn’t change over the period but the colors did as the Russians went to their distinctive olive green. The later period cossacks can also be painted with the dark blue trousers with red stripe that you see on the cossack on the right.
These and our other cossacks could be used in the Russian Civil War and right up to World War II. A simple conversion to put a PPSh in the right hand would make for an interesting figure…