The answer to the question of what is the linguistic term for the difference between concept and conception:
Yes, linguistics does have a term for such a thing, in fact, it's one of a handful of major fields of study- morphology. Simply put, it's the study of distinct units of meaning smaller than a word. That extra bit of -ion encodes a subtle difference in meaning, which is a general WAY of thinking about something, versus the specific instantiation of that idea.
Inflection doesn't encode changes in meaning per say, but specific types of information which relate words in a sentence in agreement relations, such as person and number. E.g. the subject is singular and 3rd person and this agrees with the verb in 'they cook dinner,' but 'they cooks dinner' is bad. Concept and conception are both nouns and there is no agreement relation, just a relation in meaning.
Inflection is a type of morphology, but it's much more specific. The -ti on here would be considered derivational mirohology. This type of morphology may also change a words category, e.g. help (noun) and help-ing (verb).