If the subject changes its number within a sentence but it's the same thing after all, how do I deal with this kind of ‘plurality’?

Question

Terminology clarification first. Let's say, plurality herein means the quality of being plural; the state of being plural or not, which is not the dictionary definition. I couldn't find another appropriate term for it. Well, grammatical numerity? Hmm.

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In this sentence, the number (plurality) of the subject changes at the middle of the sentence. The subject was singular, but soon becomes plural.

It's split into two and merges/merge back into one a hundred times.

We can also think of an inverted version of it. The subject was plural, but soon becomes singular.

The two are merged into one and (are)/is split back into two a hundred times.

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How do I deal with this kind of plurality? What should I assume its plurality is? Do I have to break it down into two or more sentences?

Answer 1

I would either make the verb agree with the stated subject, or introduce a new pronoun for it.

So either:

It's split into two and merges back into one a hundred times.

or

It's split into two and they merge back into one a hundred times.

(Probably the former option, because it works better with the repetitiveness of the action.)

Likewise:

The two are merged into one and split back into two a hundred times. (I agree with @sumelic that the participle helps here.)

or

The two are merged into one and that is split back into two a hundred times.

Also, I didn't do it here, but I would probably always use a comma before the phrase a hundred times in these examples.