TYPO3 Core

All extensions uses this function and for adding flexform or other extra configuration they 'hardcode' their typename.
To add flexibility the used typename could be returned in the function.

So for example the following is used to register an plugin.

// This creates the myext_display variable available in the core
ExtensionUtility::registerPlugin(
    'my_ext',
    'Display',
    'LLL:EXT:my_ext/Resources/Private/Language/locallang_be.xlf:publications.list.title'
);

// Setup flex form
$GLOBALS['TCA']['tt_content']['types']['list']['subtypes_excludelist']['myext_display'] = 'layout, select_key';
$GLOBALS['TCA']['tt_content']['types']['list']['subtypes_addlist']['myext_display'] = 'pi_flexform';
ExtensionManagementUtility::addPiFlexFormValue(
    'myext_display',
    'FILE:EXT:my_ext/Configuration/FlexForm/List.xml'
);

While the following would be slightly better and flexible.

$type = ExtensionUtility::registerPlugin(
    'my_ext',
    'Display',
    'LLL:EXT:my_ext/Resources/Private/Language/locallang_be.xlf:publications.list.title'
);

if (!empty($type)) {
    // Setup flex form
    $GLOBALS['TCA']['tt_content']['types']['list']['subtypes_excludelist'][$type] = 'layout, select_key';
    $GLOBALS['TCA']['tt_content']['types']['list']['subtypes_addlist'][$type] = 'pi_flexform';
    ExtensionManagementUtility::addPiFlexFormValue(
        $type,
        'FILE:EXT:my_ext/Configuration/FlexForm/List.xml'
    );
}