Превышение сметы меняет коммерческое предложение.

Because превышение is a noun meaning exceeding / overrun / excess, and nouns of this type often take the thing affected in the genitive.

Compare:

• превысить смету = to exceed the estimate
  
  • here смету is accusative, because it is the direct object of a verb
• превышение сметы = the exceeding of the estimate / estimate overrun
  
  • here сметы is genitive, because it depends on a noun

This is a very common pattern in Russian with action nouns.

The subject is the whole phrase Превышение сметы.

The head word is превышение, and сметы depends on it. So the sentence structure is:

• Превышение сметы = subject
• меняет = verb
• коммерческое предложение = object

So literally, it is The estimate overrun changes the commercial proposal/offer.

Because the subject, превышение, is singular.

Превышение is a singular neuter noun, so the verb must also be in singular:

• превышение меняет = the overrun changes

If the subject were plural, you would get:

• превышения меняют = overruns change

It is in the accusative case, because it is the direct object of меняет.

However, for inanimate neuter nouns, the accusative looks exactly like the nominative. So:

• nominative: коммерческое предложение
• accusative: коммерческое предложение

That is why it looks unchanged.

Because предложение is:

• neuter
• singular
• here, accusative (which looks the same as nominative for inanimate neuter nouns)

So the adjective must match it:

• коммерческое предложение

This is normal adjective-noun agreement in Russian:

• gender
• number
• case

all have to match.

Меняет is the 3rd person singular present tense of менять, an imperfective verb.

In context, it can mean:

• changes
• is changing
• sometimes more loosely, affects / alters

Because it is imperfective, it presents the action as a process, fact, or general result, not as a single completed event.

A perfective alternative would be something like изменит or поменяет, depending on the context and nuance.

Not quite. Смета usually means a cost estimate, project estimate, or itemized budget calculation, especially in business, construction, contracts, or project planning.

So превышение сметы is often best understood as:

• cost overrun
• budget overrun
• exceeding the estimate

It is usually more specific than the general English word budget.

It can literally mean commercial proposal, but in business Russian it often has a more specific meaning such as:

• commercial offer
• sales offer
• quotation
• business proposal

So depending on context, a very natural English rendering may be something like offer or quote, not necessarily the more formal-sounding commercial proposal.

Yes, Russian word order is flexible, but changing it can affect emphasis and sometimes clarity.

The given order:

• Превышение сметы меняет коммерческое предложение

is the most straightforward way to present:

• subject → verb → object

One important point here is that both превышение and предложение are neuter singular inanimate nouns, so nominative and accusative forms can look the same. That means word order and context help the reader understand who is doing what.

So while Russian allows different word orders, this sentence is clearest in the form you were given.

Because Russian has no articles.

Russian does not have direct equivalents of a/an and the as regular grammar words. Whether something is definite or indefinite is usually understood from:

• context
• word order
• emphasis
• the situation being discussed

So Превышение сметы меняет коммерческое предложение could be understood in English as:

• An estimate overrun changes the commercial offer
• The estimate overrun changes the commercial offer

depending on context.

It is a verbal noun (also called a deverbal noun) formed from the idea of the verb превысить / превышать.

So instead of saying:

• смета превышает... or кто-то превышает смету

Russian uses the noun:

• превышение = exceeding / overrun / excess

This is very common in formal or business-style Russian. Russian often uses abstract nouns like this where English might prefer a more verbal phrasing.