$extensionName = t3lib_div::underscoredToUpperCamelCase($_EXTKEY);

$pluginSignature = strtolower($extensionName) . '_nameFrontentPlugin';
$TCA['tt_content']['types']['list']['subtypes_addlist'][$pluginSignature] = 'pi_flexform';
t3lib_extMgm::addPiFlexFormValue($pluginSignature, 'FILE:EXT:'.$_EXTKEY.'/Configuration/FlexForms/FlexForm.xml');



//Zugriff auf Werte aus Flexform
$einWert = $this->settings['flexform']['einstiegUid'];

<T3DataStructure>
<meta>
<langDisable>1</langDisable>
</meta>
<sheets>
<sDEF>
<ROOT>
<TCEforms>
<sheetTitle>Konfiguration</sheetTitle>
</TCEforms>
<type>array</type>
<el>
<settings.flexform.einstiegUid>
<TCEforms>
<label>Bereich für Einstiegspunkt auswählen</label>
<config>
<type>group</type>
<internal_type>db</internal_type>
<allowed>tx_wininstitutions_domain_model_klarsicht</allowed>
<size>1</size>
<maxitems>1</maxitems>
<minitems>1</minitems>
<show_thumbs>1</show_thumbs>
</config>
</TCEforms>
</settings.flexform.einstiegUid>
</el>
</ROOT>
</sDEF>
</sheets>
</T3DataStructure>

Extbase: Extension per FlexForms konfigurierbar machen

TYPO3