There is no published guidance for what types of CTR errors demand an amendment. Only field examiners claim an innate level of wisdom on this point.
In all circumstances: Either amend it or call the Helpline and see if they will tell you that in your specific fact situation it is unnecessary. (I doubt you are going to hear that.)
As suggested, the effort put into using the NAICS codes is wasted. Being forced to used the codes on the drop down list involves too much complexity when all you are delivering is a generalization rather than a specific industry. The FinCEN guidance saying you can simply describe the business in the occupation field instead is clear.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.