Hello! Good day to all! 
I'm making this thread because I don't fully understand what the Actor feat does for Changelings.

From my perspective, the pairing of Shapechanger, ability of the Changeling, and the Actor feat feels redundant. Or, I'm not understanding the significance in this pairing.

It lists here from the official edition of Eberron, the description of the Shapechanger Changeling feature states as the following:

"As an action, _'you change your appearance and your voice'_. You determine the specifics of the changes, including you coloration, hair length, and sex.
You can adjust your height and weight, but not so much that your size changes. You can make yourself appear as a member of another race, though none of your game statistics change.
You can't duplicate the appearance of a creature you've never seen, and you must adopt a form that has the same basic arrangement of limbs that you have.
Your clothing and equipment aren't changed by this trait. You stay in the new form until you use an action to revert to your true form or until you die."

'you change your appearance and your voice', That's what it states, so you replicate the sound of the person already as a Changeling. 

From the description of the Actor feat read off of the official edition of the Player's Handbook, state as the following:

"Skilled at mimicry and dramatics, you gain the following benefits:

• Increase your Charisma score by 1, to a maximum of 20.
• You have advantage on Charisma (Deception and Charisma (Performance) checks when trying to pass yourself off as a different person.
• _'You can mimic the speech of another person or the sounds made by other creatures.'_ You must have heard the person speaking,
  or hear the creature make the sound for at least 1 minute. A successful Wisdom (Insight) check contested by your Charisma (Deception) check
  allows a listener to determine that the effect is faked."

'You can mimic the speech of another person or the sounds made by other creatures', is a bigger way in my perspective in saying, 'you change your appearance and your voice'. 

So answer my this everyone, how does this feat impact the Changeling feature in a significant way that I cannot see?

This thread's purpose is to not contradict the rules of the game, its purpose is to discuss the understanding between the lines of these features according to the rules.

I'll look forward to hearing your explanations from all of you so I can prepare this character I'm excited to play as!

Eagerly awaiting, Scrub.

In short, they compliment each other, as each give you something the other doesn't. Shapechanger allows you to replicate the look and sound of someone you've observed rather than simply "mimic" them; while the actor feat gives you the mechanical benefits of being able to pass yourself off, not just as a member of a specific race but a specific person in particular, such as mannerisms, speech patterns that you would not gain from the physical transformation that Shapechanger allows you.

Oh! That makes sense! So when changing into a new person, you gain the ability to speak but you don't behave the same way they would. Like you brush your teeth the same way as the person you would change. Okay, now I understand!

Now, I'd like to go ask in-depth questions on character creation for a bit, now that I know I really want this feat as soon as possible.

1: When making a Changeling, can you start the session#1/campaign, already knowing identities out the gate as a Changeling. Like, can you not start the game as the true form of a Changeling and be a person my character already knew, plus change appearances and clothing later on, when given the chance. Is that allowed?

2: When you choose to forgo ability score bonuses from the Changeling (+2 to Charisma and junk) can you choose to get a feat and pick up the Actor feat @ lvl 1?

Thank you for commenting so fast, that was a great explanation! But can you answer these questions as well?

Thanks in advance, Scrub.

1. You need to discuss with your DM to figure out what identities you might start with.  It will depend on your backstory and the world the DM is using.

2. Typically it is just switching out fixed ability bonuses (+2 CHA) for more flexibility (+2 to one ability or +1 to two different abilities, of your choice).  It would be up to your DM to allow you to take a Feat instead.

As Gruntler has already stated, both are really questions/discussion for your DM, but generally using custom lineages, gaining a feat would take the place of race specific boons like Shapechanger rather than the ASI. 

Thank you! That just about wraps up all my questions! 

Thank you both @DarkAlGhul & @Gruntler for clarifying in this thread.

You've made my day, Scrub.

Take the Charlatan background!

You have created a second identity that includes documentation, established acquaintances, and disguises that allow you to assume that persona. Additionally, you can forge documents including official papers and personal letters, as long as you have seen an example of the kind of document or the handwriting you are trying to copy.