In the UK you can "be known" as anything you want and request to be referred to by that name by any trade or legal body.
There are two option if you wish legal proof of a change of name Statutory Declaration which can be done by a witnessed signature from a Justice of the peace or a Magistrate (for which they may charge a fee), or else registration by Deed Poll at a cost of £15 that officially records your request to be "known as" superseding your birth registered name.
You may use any combination of the names with which you were registered at birth with no necessity for legalities, you may also use your mothers maiden name without a legal formality, likewise you may change your name to the family name of your spouse or use both family names with a hyphen.

My son for example uses his middle name and surname rather than his first name out of preference, my other son formerly my daughter changed names after gender reassignment by deed poll but was known by that name for several years prior.

In Texas, you have to go through the legal stuff. I can't believe it would be different anywhere else.

Yes....I think you do if you want to use it as your "legal name". And it's not easy to do these days. I found out when I got married 10 years or so ago....after 9/11, they got stricter about everything involving identity. It $400 or more now, if I wanted to change my last name to my husband's. After my first marriage 30 years ago, I just had to show the marriage certificate at the DMV. So simple. Now, you have to have a full background check with fingerprints etc. They search through NCIC to be sure you're not stealing someone's identity. I don't think you will be able to get your ID or credit cards changed without going to court and all the hassle.

It varies by state. In CA you can live under any name you want as long as it isn't fraudulent. You may run into problems without a legal name change though when it's time to get a passport.

You can be anyone you want as long as you're not defrauding anyone. So for instance if you stop paying taxes under your old name or have debts that you ignore that's illegal. Otherwise you can be anyone you want. You can make it legal but you don't have to. You might have to get a Social Security card in a different name Etc but as long as you're not breaking any laws you can do whatever you want.

Do a search for your county's court system. There are likely to be links to documents you can print out and fill out yourself. You should also be able to find out filing costs too.

Thank you all for your comments/replies to my question. ? The consensus seems to be that I will need to do it legally and save myself trouble down the line.

I've looked into it further and filling out the forms and going to court so I can change my name on my drivers license and social security cards etc. and have the documents for all the other things is the safest way to go.

I haven't found any information on how much it will cost but I'm guessing that a couple of hundred dollars or so is probably right.

U have a legal name, what U were given @ birth. I changed my first name in 1989 in court. I always use my changed name when speaking . Sometimes on forms, however, I must use a legal name, like on drivers license & credit cards. That name from Birth comes out.

Yep, ‘fraid so.

My brother did that when he got into his music career and he did have to go through the legal hoops.

Has to be done "Legally" Even in the circumstances you have mentioned.

Switched my first and middle name around legally. It was really quite easy. Filled out the forms and posted in the court house for 10 days. Easy Peasy

Yes and no. If you want to drop your last name from bank accounts, SS, Driver's License, other licenses, Passport, deeds, mortgages, car registration, insurance, taxes, etc. then you MUST go through the legal channels.

If you just want to do it casually, there is no issue as long as it's not for fraud purposes.

You are free to do anything you want to do, but it could have repercussion at some point. A lot of people use aliases.

Remember you have legal documents associated with your last name. I could cause some legal confusion at some point down the line unless a legal name change is done.

I don't know.... Depends which country you live in.