Rusty Autolisper needs help

Ignore previous thread... I've been attempting to use entmod to edit the end of a line... I am successful in using the subst command to modify the startpoint of a line,,,, but when I try to use entmod to update the list, the output gives me the original list. Any help greatly appreciated. Does entmod not work on lists that represent coordinates?

(setq ent (car (entsel))) (setq alist(entget ent)) (subst (list 10 1.0 1.0 0.0) (assoc 10 alist) alist); list shows up with new starting coordinate (entmod alist); original alist with original starting coordinate shows up.

Thanks in advance.

Thankyou for the tip.