lost calc feature in LO

Dear Experts of LibreOffice,

having started work at LHMuenchen in the development departement with 
focus on LibreOffice under LiMux/kubuntu my current task is to 
reactivate a deactivated feature within calc which again is supposed to 
allow DDE link in addition to the newer and current external file link.

Though the construction of DDE link still works, as long as I replace 
file link functionality.
But otherwise the additional switch DDE link vs. file link rises to 
become a problem to me where to place the switch in the depth.
I did not find a single or definite interface for all the selections to 
insert a value and the still existent decision is controlled not only by 
a define
SotClipboardFormatId::LINK
but at least a text string
OUString aExtraBits("calc:extref")
and some other hidden data.
I would be glad to obtain a hint where to find some more locations of 
decision. Can anyone help me ?

Best regards,
Andreas
--
Andreas Baier
E-Mail: aba.baier@web.de
Munich, Germany