On one of the sites I am a member of I can set my nickname for a chat window. The nickname in the chat window has a decent character limit.
In the settings for the site itself I am restricted to a maximum of 15 characters, which is an annoyance and an inconsistency.
Editing the webpage in Chrome (or Chromium) can be done by right-clicking on the element (in my case the text field) and clicking “Inspect” on the popup menu.
A new window will open on the right of the webpage. At the top will be a line reading
Elements Console Sources Network
Click on “Sources”.
As there was a dialogue alert box displayed, we can do a search for the text of the message.
Press Ctrl-F (Find) and type in the alert message, in my case:
“Chat Nick Name can take a maximum”
Somewhere right above that will be the code you need to amend (at least in my case).
Find the code you need to change, change it to what you need.