How do you form -able words? Which root do you have to attach the suffix to in order to make the new word?
For example, is the word 'restrictionable' correct?
restriction + -able ⇒ 'that may or should be restricted'?
We can freely make new adjectives from verbs using the suffix -able. It does not matter at all whether these words have ever been used before. It does not matter if these words are in the dictionary or not. Anybody can understand these words as long as they understand the verb involved. When we can use a suffix like this, we call it a productive suffix. We can have productive prefixes too.
The suffix -able is a productive suffix. We use it to turn verbs into adjectives. However, there are a few restrictions:
So think of any transitive verb you like, stick an -able on the end of it, and you'll almost definitely have a nice, perfectly formed adjective:
The Original Poster's example
We can definitely use the word restrictable. The problem with the word restrictionable is that the base word, restriction, is a noun, not a verb. For this reason the adjective restrictionable will probably not work for the OP's needs.
However, if some company or other uses the word restriction like a verb as part of their jargon, then they could also freely use the word restrictionable as an adjective too!
-Able/-ible goes on the ends of verbs, not nouns. Many words in English work as both verbs and nouns. However, if the -ion suffix on a word was used to turn a word into a noun, awkwardness can happen.
But really English with its grammar lets you use any word in many parts of speech even if they are not "supposed" to be used in such a way. Some words not commonly used in this way will sound weird, but it'd be rare for it to sound so weird that someone couldn't figure out what you meant.
Restrict is a verb. Restrict-ion is a noun-ified version of restrict meaning instance or event of being restricted or something that causes or maintains a state of being restricted.
So, can you use restriction as a verb? It's not common, but possible. The meaning won't substitute exactly for restrict.
Here's a contrived example that may not ever had been said at someone in reality, but I could image it happening:
A: I think Jon over there is on restriction and can't do the task.
B: Who restrictioned him?
A: His boss, well, really his doctor.
B: Ok, find me someone who's not on restriction and get it done.
Here, restrictioned means placed on restriction - and if it sounds/feels like a made-up word, it is, but it does follow the rules. Furthermore notice the above is a workplace/business setting where this type of thing might happen more often than not. Anyway, on restriction here means he is marked in some system or list as being restricted from a task - but restrict means prevent from doing something.
So to answer your question, -able/-ible is put on the same form of a verb that you'd use for the infinitive.
In informal English, you can coin masses of new words where they won't have a formal definition, but your readers/listeners will know instinctively what you mean.
I know that by restrictionable - you mean "is able to be restricted".
Particularly with the suffix -able, we can append this to just about any word to mean "able to do ..", and you'll find native speakers often do! We usually keep the hyphen in place for words that we know aren't "real" words.
Most words, particularly verbs are suffix-able with -able.
We set up the tent on the most camp-able ground we could find, but it was still a bit uncomfortable.
My friend is so embarrass-able. Just one mention of his school nickname turned him bright pink.