Don’t worry you can change it once you page have at least 25 fans. Just visit Facebook Username Page and you will see something like this.
Now choose the Page you want to customize and type the custom short name in the box to check the availability . For example, i type Bein2 in the box above. If the name available, a pops up will come out. Read and confirm the disclaimer that pops up. See the image below.
Now you are done and a success pop up will come out, see the image below.
To view the changes just visit your fan page and you will see your Facebook page Url already change. For example see our new Facebook Page Url below.
It advisable to write down the old URL since the numeric string is the page ID number and you may need it in future for reference purposes.Keep in mind, similar to Page titles, the Username can only ever be set once and can not have Username which already in use by your page or another user.