The subject is not necessarily meant to be a literal question, but rather an example of creating words that have an apparently obvious meaning through prefixes, suffixes, using various parts of speech as other parts (nouns as verbs, for example), and so on, in order to get one’s meaning across. Is doing so creating what people would consider “actual words”?
Consider, for instance, the adjective candid. Merriam-Webster’s online dictionary graces us with the adverb, candidly, and a noun, candidness. But what about, for example, candiditious, “relating to candor”? Or candiditiousness, “The state of relating to candor”? Candidity? Are these in some way valid constructions in that they are “really” words, or are they only words in the sense that we can understand them through their suffixes?
Words become part of the language strictly through usage. There is no official body that decides these things.
Creating a word - whether through adding on suffixes or prefixes or inventing it out of whole cloth - gives you nothing but a collection of letters. There are names for such inventions - coinages, neologisms, nonce words - but that’s all after the fact.
If people decide an invention is useful, they will use it. It then becomes a word. It may be considered slang, argot, colloquial, or formal, depending on when and how it is used. Eventually, if enough people use it in a consistent fashion, it may even enter the dictionary. But note that most dictionaries, even “unabridged” ones, don’t bother to keep track of all the possible variations on a word that are possible by adding suffixes. It’s just assumed that if the need arises, the proper form will be used.
There are certain formations that are considered more proper, in the sense that they are consistent with the ways words have historically been formed. Even so, words that don’t follow these “rules” occasionally become part of the language, and there’s nothing the pedants can do about it, except not use them.
English is a marvelous language precisely because it is so flexible. Ignore anyone who says that these coinages are ruining the language. They were saying that 100 years and 100,000 coinages ago too.
There is the term “nominalize”, which means to make a word that’s another part of speech a noun. For example, the word “funny” is often used as a noun- “I made a funny”, so it’s been nominalized.
Just don’t let it go too far too quickly, or s’ekh vyerál ßandai fteghrannion audh xetu!
So is there a word for “make bigger” in various contexts, but largen is not considered a normal word to use, possibly enlarge would be used instead. But the -en is a verb suffix for use with adjectives, so largen seems like it should be grammatically valid. Similarly, the -ify, when used with nouns, would mean “invest with the properties of”, so nounify seems like a perfectly valid “word”, even if a synonym already exists. Other than convention, what would compell me to use “nominalize” over “nounify”? You see what I mean?
Other than convention, what would compell me to use “nominalize” over “nounify”? You see what I mean?
I do and actually though I’ve never seen either “word” before, I knew immediately what “nounify” meant (At least what you meant it to mean). “Nominalize” on the other hand I would have taken to mean “make nominal” which could have different meanings in different contexts depending on what nominal meant in that context. In no context would I have thought it meant to “make a noun” of something.
Ask Sam Clem. He’s a coincollector. 
Convention is itself enough to make you make the choice, OldGuy. Convention is exactly what allows you to immediately understand what “nounify” means. Convention is an amalgamation of the rules of the grammar of the language and the standards of diction and rhetoric that you’ve encountered all your life as a living speaker.
Children are estimated to learn up to 100 new words a day throughout their schooling, and most of these are obviously not learned in school. Without convention there would be no way to sort out what are accepted words and what are solecisms made by those still learning the language.
I don’t know about ‘nounification’ but I’ve certainly coined, or at any rate used, the word ‘verbification’ myself and never had anybody misunderstand what I mean.
Kinda the opposite of the OP, but any discussion is better with a Calvin & Hobbes quote:
Verbing weirds language.