No matter the era or conflict soldiers find solutions. The Legion veterans who served in WW I and the RIF Wars taught me how to really care for my feet.
From "A Manual for Military Surgery, " by Julian J. Chisolm M.D., Surgeon CS Army, 3rd Edition, Columbia 1864
During the mid-day rest, if any opportunity exists, the shoes and stockings should be removed and the feet bathed, which, by removing dirt and acid secretions, will prevent excoriations. It may also be advantageous, at such times, to change the socks from one foot to the other, so the seams may come at different portions of the foot, which will prebvent continued and injurious pressure. Soaping the sock will also prevent excoriations, and add much to the comfort of a soldier while on the march.
I found no mention of the topic in the first edition of Chisolm which was published in 1861.
Here's Robert Carter (22nd MA) writing home in May 1863. Seems the soap trick got around:
"A soldier knows how to take care of his feet if he has time. * * * I knew, before, the recipe for keeping the feet in good order by rubbing the stockings with bar soap; have tried it a great many times; it is a great thing."
https://archive.org/details/cu31924032780623