Learn Farsi: فرضاً که یک تداخل رخ بدهد؛ کاش ماشین زمان را دستکاری نکرده بودیم. - Let us assume that an interference occurs; I wish we had not tampered with the time machine.

The phrase فرضاً که (assuming that / let us assume that) sets up a hypothetical scenario. In Farsi, when you introduce an assumed condition or uncertain future event using this type of conjunction, the verb that follows must take the subjunctive mood. Here, رخ بدهد is the present subjunctive of the compound verb رخ دادن (to occur).

What is the function of the -اً ending on the word فرضاً?

The suffix -اً (pronounced "-an") is a grammatical borrowing from Arabic. In Farsi, it is very commonly used to turn a noun or an adjective into an adverb. Here, the noun فرض (assumption) becomes فرضاً (hypothetically / by assumption).

Why is the second verb, دستکاری نکرده بودیم, in the past perfect (pluperfect) tense?

The word کاش (I wish) is used to express a strong desire or regret. When you are expressing a wish about something that already happened in the past—meaning it is contrary to reality or an unrealized past condition—Farsi requires the past perfect tense. Since they are regretting an action they already did, they use دستکاری نکرده بودیم (we had not tampered).

Since the first part of the sentence is just a hypothetical assumption, why do we use the definite object marker را after ماشین زمان?

While the interference is hypothetical, the time machine itself is a specific, known entity in the context of the sentence (the one they built/used). Because ماشین زمان is the specific direct object receiving the action of "tampering," it still requires the definite marker .