it's possbile that typo3 stays updatable. You have to create the original path in your file-structure:
/httpdocs/fileadmin/Templates/fluid_styled_content/Resources/Private/Partials/Header
You can simply copy the Header.html and paste it in there. In the Header.html you can edit the switch-case an create new Layouts.
Then yo have to edit your template in the backend. You can do this by clicking on "Template" and then "Edit the whole template record". Include the following snippet in "Setup":
lib.fluidContent.partialRootPaths.100 = fileadmin/Templates/fluid_styled_content/Resources/Private/Partials/
After you created the path you have to edit the page properties in the backend. Under "Resources" > "Page TSConfig" you can create your label for the backend, e.g.:
TCEFORM.tt_content.header_layout {
addItems.6 = Slider-Title
}