Is it possible to prevent saponification by modifying free fatty acids?
In principle You can replace the Sodium ion with any other cation. But all You get is another kind of soap: Potassium gives a smoother substance, Calcium/magnesium gives the soap-stone you see in washing machines, etc.

Another possibility is to esterify the fatty acid with an alcohol. This is widely used in the industry to produce non-ionic surfactants, and these do not react with cations. But off course, then it really isn’t a fatty acid anymore.