Try this on the 4000:
DELETE-ACTDA TYPE=<param>,STNO=<number>,
FEATCD=FWD,[CFVAR=<param>],[DTYPE=<param>],
[ITYPE=<param>],[SI=<param>];
| FEATCD=DND
So in your case:
DELETE-ACTDA:STN,1234,FWD;
(with 1234 being replaced by the extension in question).