Learn Hardcore Norwegian: Planen vår er fleksibel slik at vi kan endre den i morgen. - Our plan is flexible so that we can change it tomorrow.

Postposed possessive (after the noun):
- planen vår = our plan (the plan of ours, specific)
- Pattern: [definite noun] + [possessive]
- Example: boka mi (my book), huset deres (their house)
Preposed possessive (before the noun):
- vår plan = our plan (more like “our plan” as opposed to someone else’s)
- Pattern: [possessive] + [indefinite noun]
- Example: min bok (my book), deres hus (their house)

You cannot mix these patterns, so vår planen is ungrammatical. It must be either:

Planen vår
or
Vår plan

Can I also say Vår plan er fleksibel? Is there any difference in meaning?

Yes, you can say Vår plan er fleksibel, and it is grammatically correct.

The difference is mainly nuance:

Planen vår er fleksibel
- Neutral, everyday way to say “our plan is flexible”.
- Focus is slightly more on the plan itself.
Vår plan er fleksibel
- Sounds a bit more formal, written, or contrastive.
- Can sound like “Our plan (as opposed to others) is flexible.”

So both are correct; in normal speech Planen vår is more common and neutral.

Should there be a comma before slik at in this sentence?

According to standard modern comma rules in Norwegian, you would usually write:

Planen vår er fleksibel, slik at vi kan endre den i morgen.

because slik at introduces a subordinate clause.

However:

In real-life informal writing, Norwegians often omit this comma, especially in short, simple sentences like this one.
In formal writing (essays, reports, etc.), it is safer to include the comma.

So the strictly “correct” version is with a comma, but you will often see it without, as in your example.

What exactly does slik at mean here, and how is it different from så or for at?

In this sentence, slik at means “so that” and introduces a clause of result/purpose:

Planen vår er fleksibel slik at vi kan endre den i morgen.
→ Our plan is flexible so that we can change it tomorrow.

Comparison:

slik at
- Often: result or practical consequence
- “in such a way that / so that”
- Neutral, a bit more written/formal than sånn at
så (at)
- så vi kan endre den i morgen is more colloquial.
- Often used in speech instead of slik at.
- Meaning here: “so (that) we can change it tomorrow.”
for at
- More clearly expresses intention/purpose (“in order that”)
- Planen vår er fleksibel for at vi skal kunne endre den i morgen.
  = Our plan is flexible in order for us to be able to change it tomorrow.
- Slightly more formal/explicit purpose.

In your sentence, slik at nicely expresses that the flexibility of the plan makes it possible to change it tomorrow.

Why is it vi kan endre den and not kan vi endre den?

Because vi kan endre den is inside a subordinate clause introduced by slik at.

Norwegian word order rules:

Main clause (statement): the finite verb is normally in second position (V2).
- Vi kan endre den. (We can change it.)
- I morgen kan vi endre den.
Yes/no question: verb comes before the subject.
- Kan vi endre den? (Can we change it?)
Subordinate clause: subject comes before the finite verb.
- Introduced by at, fordi, hvis, når, slik at, etc.
- … slik at vi kan endre den i morgen.

So kan vi endre den would sound like a question, which is not intended here.

Why is the pronoun den used here, and not det or repeating planen?

The pronoun den refers back to planen:

plan is a masculine noun: en plan – planen
The corresponding object pronoun is den:
- Jeg liker planen. Jeg liker den.
- Vi kan endre planen. Vi kan endre den.

If the noun were neuter (et hus – huset), you would use det:

Huset er fleksibelt slik at vi kan endre det i morgen.

Why not repeat planen?

You could say … slik at vi kan endre planen i morgen, but in good style you usually avoid repeating the noun and use a pronoun when it’s clear what you mean.
Unlike English, you can’t just drop the object:
- ✗ slik at vi kan endre i morgen is wrong; endre needs an object here.

So den is the natural object pronoun for planen.

Why is the adjective fleksibel and not fleksibelt or fleksible?

Adjectives in Norwegian change form depending on gender, number, and definiteness.
In Planen vår er fleksibel, the subject is:

planen vår = masculine (or common gender), singular, definite

For predicative adjectives (after er, blir, virker, etc.), the patterns are:

Masculine/feminine singular: fleksibel
- Planen vår er fleksibel.
- Boka er fleksibel. (a silly example, but grammatically correct)
Neuter singular: fleksibelt
- Systemet er fleksibelt. (et system)
Plural (all genders): fleksible
- Planene våre er fleksible.
- Ordningene er fleksible.

Since planen vår is singular, non‑neuter, the correct form is fleksibel.

Why is there no å before endre? Could I say kan å endre?

You should not use å after modal verbs in Norwegian.

Common modal verbs: kan, vil, skal, må, bør, får.
They are followed by a bare infinitive (without å):

vi kan endre den (we can change it)
jeg vil spise nå (I want to eat now)
hun skal reise i morgen (she will travel tomorrow)
jeg må jobbe (I must work)

With normal (non-modal) verbs, you usually use å + infinitive:

jeg liker å endre planer (I like to change plans)
det er viktig å være fleksibel (it is important to be flexible)

So:

✓ vi kan endre den
✗ vi kan å endre den (incorrect)

What is the difference between endre and forandre here? Could I say forandre den?

Both endre and forandre can mean “to change”, and often they are interchangeable.

In this sentence, you could also say:

Planen vår er fleksibel slik at vi kan forandre den i morgen.

General tendencies:

endre
- Slightly more neutral and common in formal or technical contexts:
  - endre planen, endre innstillingene, endre loven
forandre
- Often used about more general or personal changes:
  - forandre seg, forandre livet sitt, forandre mening

But this distinction is not strict, and Norwegians use both verbs quite freely. Here, endre is maybe a bit more natural with planen, but forandre is also fine.

Why do we use the present tense (er, kan endre) when talking about i morgen (tomorrow)?

In Norwegian, the present tense is very often used to talk about the future, as long as there is a time expression that makes the meaning clear:

Planen vår er fleksibel slik at vi kan endre den i morgen.
= Our plan is flexible so that we can change it tomorrow.

Other examples:

Jeg reiser i morgen. (I’m leaving tomorrow.)
Vi møtes neste uke. (We’ll meet next week.)

You can also use skal for future, but it’s not necessary here:

Vi skal endre den i morgen. (We are going to change it tomorrow.)

So the present tense + i morgen is the normal way to talk about a near-future action.

Does i morgen mean “in the morning” or “tomorrow”? How is that different from på morgenen or om morgenen?

This is an important distinction:

i morgen
- Means “tomorrow” (the whole next day)
- Not “in the morning”
- Vi kan endre den i morgen. = We can change it tomorrow.
morgen (without i)
- Means “morning”
- om morgenen / på morgenen = “in the morning” (in general or on a given day)
  - Jeg jobber best om morgenen. (I work best in the morning.)
  - Vi kan endre den i morgen tidlig. (We can change it early tomorrow morning.)

So in your sentence, i morgen clearly means “tomorrow”, not “in the morning”.