Giyim tarzını değiştirdiğinden beri kendini daha rahat ve cesur hissediyorsun, değil mi?

It means since you changed or ever since you changed.

The important part is -den beri, which expresses a starting point in the past that continues up to now.

So the sentence is talking about an ongoing result:

• you changed your clothing style in the past
• from that time until now, you feel more comfortable and bold

A useful comparison:

• -den sonra = after
• -den beri = since

So here beri is the better choice because the feeling continues into the present.

It breaks down like this:

• değiştir- = to change something
• -dik / -diğ- = a verbal noun / subordinating suffix
• -in = your / marks the subject as you
• -den = from, since

So değiştirdiğinden beri literally works something like:

• from your having changed
• more naturally: since you changed

This is a very common Turkish way to build time clauses.

Because giyim tarzını is a direct object, so the verb needs to be transitive.

• değişmek = to change, to become different
• değiştirmek = to change something

In this sentence, the person is changing their clothing style, so Turkish uses değiştirmek.

Compare:

• Tarzın değişti. = Your style changed.
• Tarzını değiştirdin. = You changed your style.

Because it is the direct object of değiştirmek.

The base expression is:

• giyim tarzı = clothing style / style of dress

This is a noun compound in Turkish, so tarzı already has a compound ending. When you add the accusative, it becomes:

• giyim tarzını = the clothing style, as the object

You can think of it like this:

• giyim tarzı = clothing style
• giyim tarzını değiştirmek = to change one’s clothing style

So the -nı here is part of the object marking.

Because Turkish usually does not need subject pronouns when the verb already shows the person.

Here, hissediyorsun tells you the subject is you:

• -sun = you

And inside değiştirdiğinden, the -in also points to you in the subordinate clause.

So sen is unnecessary unless you want extra emphasis.

Because Turkish often says to feel yourself + adjective.

So:

• kendini rahat hissetmek = to feel comfortable
• kendini iyi hissetmek = to feel well
• kendini yorgun hissetmek = to feel tired

That is very normal Turkish.

Literally, kendini means yourself, and it is in the accusative because it is the object of hissetmek.

English usually just says you feel comfortable, but Turkish commonly says you feel yourself comfortable.

Because the sentence describes a state that is still true now.

• hissediyorsun = you are feeling / you feel
• this suggests an ongoing present situation

That matches -den beri, which also points to something continuing from the past until now.

If you used a simple past form like hissettin, it would sound like a completed event in the past, not an ongoing result.

Yes. In this sentence, daha naturally applies to both adjectives:

• daha rahat ve cesur = more comfortable and bolder / more confident

Turkish often lets one daha cover both items in a pair.

If someone wanted extra emphasis, they could repeat it, but that is not necessary here.

It is a tag question, like:

• right?
• isn’t that so?
• haven’t you? depending on context

So the whole sentence is not just a statement. It is checking for agreement.

This is very common in Turkish conversation.

A useful thing to know: in this use, değil mi? is often attached to the whole sentence as a general confirmation tag, not as a literal negation of the main verb.

No, but this order is very natural.

The sentence is organized like this:

• Giyim tarzını değiştirdiğinden beri = time expression
• kendini daha rahat ve cesur hissediyorsun = main statement
• değil mi? = tag question

Turkish often puts time expressions near the beginning of the sentence, especially when they set the scene for everything that follows.

So this word order sounds smooth and typical.

Yes, you may hear both.

• değiştirdiğinden beri explicitly marks the subject inside the clause: since you changed
• değiştirdikten beri also means since changing / since you changed

In this sentence, değiştirdiğinden beri is very clear because it directly encodes you inside the subordinate clause. That makes it especially neat here.

Both patterns are useful, but the one in your sentence is a very common and natural way to say it.