[TYPO3] Extend a existing extension BE form with your own fields

[Jeroen Visser]

Hi,
I need to extend the BE form off a existing extension with a field. I 
have created an extension with kickstarter and thought to add it to the 
tca.php of the existing extension by writing this in my own tca.php:

$tempColumns = array(....
);

t3lib_div::loadTCA("tx_dmmjobcontrol_job");
t3lib_extMgm::addTCAcolumns("tx_dmmjobcontrol_job",$tempColumns,1);
t3lib_extMgm::addToAllTCAtypes("tx_dmmjobcontrol_job",",--div--;Event 
Info,tx_mblnewsevent_isevent;;;;1-1-1, tx_mblnewsevent_from, 
tx_mblnewsevent_to;;1, tx_mblnewsevent_where;;2, 
tx_mblnewsevent_organizer");

I don't get the expected result in the BE form. I tested it by adding it 
directly in the TCA of the extension to expand, nothing happened ass well.

So the question is: How can I add my own fields to the BE form of a 
existing extension.
Thank's in advance,

Regards,
Jeroen