A terv egyelőre jó, de holnap még változhat.

A is the definite article, meaning the.

• a terv = the plan
• Hungarian has two forms of the:
  • a before a consonant
  • az before a vowel

Since terv starts with t, it takes a.

In Hungarian, the verb to be is usually left out in the present tense, third person singular.

So:

• A terv jó. = The plan is good.
• literally: The plan good.

This is completely normal in Hungarian.
You would use van in other persons or tenses, but not here:

• Én jó vagyok. = I am good.
• A terv jó volt. = The plan was good.

Egyelőre means for now, for the time being, or so far.

It often suggests that the situation is temporary and may change later. That fits this sentence very well:

• A terv egyelőre jó = The plan is fine for now

So it does not just describe the present moment; it also hints that this is not necessarily final.

A useful comparison:

• most = now
• jelenleg = currently / at present
• egyelőre = for now / for the time being

Of these, egyelőre is the best choice when something may change later.

All of those can work, depending on context.

In this sentence, jó probably means something like:

• good
• fine
• acceptable
• okay for now

So A terv egyelőre jó is not necessarily enthusiastic praise. It can simply mean:

• The plan is okay for now
• The plan works for the moment

De means but.

It connects the two parts of the sentence:

• A terv egyelőre jó = The plan is fine for now
• de holnap még változhat = but it may still change tomorrow

So de marks a contrast between the current situation and the possibility of change.

Változhat means may change or can change.

It comes from the verb változik = to change.

The ending -hat / -het often expresses:

• possibility
• ability
• sometimes permission

Here it expresses possibility:

• változhat = it may change

Because of vowel harmony, this verb takes -hat rather than -het.

So:

• változik = it changes / is changing
• változhat = it may change

Hungarian often leaves out subject pronouns when they are clear from context.

In English, you need it may change.
In Hungarian, once a terv has already been mentioned, you do not need to repeat it.

So:

• A terv egyelőre jó, de holnap még változhat.

naturally means:

• The plan is fine for now, but it may still change tomorrow.

The subject in the second clause is understood to be the plan.

Here még means something like still.

So:

• holnap még változhat = it may still change tomorrow

This adds the idea that even though the plan is good now, the matter is not settled yet.

Be careful: még has several meanings depending on context, such as:

• still
• yet
• even
• more

In this sentence, still is the best match.

Hungarian word order is flexible, but it is not random. It often reflects focus, emphasis, and information structure.

In holnap még változhat:

• holnap sets the time: tomorrow
• még adds the idea still
• változhat is the verb: may change

So the clause flows naturally as:

• tomorrow it may still change

A different order is possible, but it may shift emphasis slightly. For example:

• Még holnap is változhat would emphasize that the possibility extends even into tomorrow
• Holnap változhat még sounds less neutral and may feel more marked depending on context

The original sentence sounds natural and neutral.

Because Hungarian, like English, often avoids repeating the subject when it is already obvious.

So instead of saying:

• A terv egyelőre jó, de a terv holnap még változhat.

Hungarian normally says:

• A terv egyelőre jó, de holnap még változhat.

The second a terv would usually sound unnecessary unless you wanted special emphasis.

Yes, but the nuance changes.

• változhat = may change
• megváltozhat = may undergo a change / may become changed / may change significantly

The prefix meg- often gives the verb a more completed or result-oriented feel.

So:

• változhat is a general, neutral may change
• megváltozhat can sound a bit more like may end up changing

In your sentence, változhat is the more neutral and natural choice.

It is fairly neutral and natural. It works in both spoken and written Hungarian.

• A terv = neutral
• egyelőre = common and natural
• változhat = standard

So the whole sentence sounds like normal, everyday Hungarian, not especially formal and not slangy.