[TYPO3] TCA: change behiavour of select form

[Daniel]

Hi to all,

does anybody what i should do to change the behiavour of the standard
TCA form in the BE of type "select" (the one used for MM relations)?

I want to add two handlers when
- an element is selected (then this options should be set to disabled
or removed)
- an element is deselected from the left selectbox (then the element
should reappear on the right selectbox)

Thanks in advance,
Daniel