Issue solved
SAP Fcodes (e.g. ICLB_SUBCLMAINT for subclaim creation) are defined in Tab. TICL096.
To make them available as pushbuttons etc. needs extra customizing in Tab. TICL098
ICLIMG -> Claim -> Technical Settings -> Process Control via Display of Function Codes -> Configure Display of Function Codes: mark entry with process='+', node cat. = '0', fcode=ICLB_SUBCLMAINT
-> go to 2nd. level "Control of FCodes for Context Menu/Push Buttons" and make a new entry