Make a child theme
 

Normally if you create a child theme, the CSS must be copied. When I do this with atahualpa, nothing happens. I think because the CSS is not in a file, but in the database.

What to do if I want a childtheme? I want to change hard-coded and DON'T overwrite that file

Any CSS you use in the theme options will NOT be over written durning a theme update becasue it is stored in the database not a theme file.

You create a child theme just like any other child theme - although I have found only a handful of situations where it was needed in the 6 years I've been using the theme.

Why I use it and how is not the question. I want to make a change to a file that would be updated when I do an update, so I want an option to hardcode some files. Isn't there any option to do this with a trick??

Just follow the directions here to create a child theme.

One thing, if you change the code of one of the theme files, and a new release updates that file (say with a bug fix) - you will not see the fix since you will still be using the old copy.

The reason I ask why you are doing it is there may be another way to do what you want using the theme options (i.e. how to have different templates? One widget sdidebar or two)

I want to create a creditpage (or write something in de about page) and so I want to remove Powered by WordPress & Atahualpa and I always use a childtheme with every theme

directions for removing the credits are avaliable in the gold forum/tutorials for users that have donated $20 or more to support the development of the theme.

I'm not removing it, but replace it. I don't want to remove it, because Atahualpa is a must for everybody!

I like Atahualpa, but want to use a theme switcher for a more accessibility theme. The other one should be also atahualpa, but only with one sidebar, bigger font-size, not colors (black and white) an less widgets. I tried a second Atahualpa folder (another version) and configured other theme options but both themes use the same options - of course from the database.
So I thought a child of atahualpa theme with external css file would be the solution. Isn't right? Or is there another solution for my problem?

The CSS is stored in the database. You can have two versions, but you will have to edit the code and change every occurance of 'bfa_ata4' to something else like 'bfa_ata5'. That's the ID of the row in the database.

There are 34 places that would have to be changed. If you have a Mac, there is a program called 'TextWrangler' (free) that allows you to do global changes to a folder - every file in the folder and sub folders are checked for the string.

I don't know if there is a windows equlivant.