you can use =.. to convert simple terms.
?- x(a,b,c) =.. A.
A = [x, a, b, c].
what about complex terms :
x(a,b(c,d)) ==> [x,a,[b,c,d]]
x(a,b(c,q(d))) ==> [x,a,[b,c,[q,d]]]
then as separate task i want to re-generate the terms with changed functor :
x(a,b(c,d)) ==> [x,a,[b,c,d]] ==> y(a,f(c,d))