[TYPO3-english] Restrict category-tree in News plugin (tx_news) by TCA

[Bert Hiddink [BENDOO e-work solutions]]

Hello,

In TYPO3 6.2.25/tx_news, I want to restrict the category-tree when 
someone edits the plugin by flexform.
However, the following:

TCEFORM.tx_news_domain_model_news.categories.config.treeConfig {
     rootUid = 2
     appearance.nonSelectableLevels = 0
}
...does not have any effect.
Any ideas?

Thanks in advance!
Bert