Can even a small inguinal hernia affect bowel movement?

Possibly. Even a small inguinal hernia can involve the colon, and thus lead to problems with bowel moments.
While. Anything is possible, a small hernia would not commonly directly affect bowel movements. However the pressure discomfort of a hernia could cause a person added discomfort if straining for constipation & make it indirectly difficult or uncomfortable to use the toilet.