(*  Remove Sin(x), itemizes expression  *)
Cases(a*Sin(x)+b*Sin(2*x)+c*Sin(5*x)+d*Sin(6*x), Sin(q_*x), 2)

(*  Remove Sin(qx) where q > 4  *)
a*Sin(x)+b*Sin(2*x)+c*Sin(5*x)+d*Sin(6*x) /. Sin(q_*x) /; 4<q :> 0

  (*  same as  *)
ReplaceAll(a*Sin(x)+b*Sin(2*x)+c*Sin(5*x)+d*Sin(6*x),
RuleDelayed(Condition(Sin(q_*x), 4<q), 0))

(*  Perform matrix transform  *)
Print({{5,3}, {6,2}, {7,1}} /. {x_, y_} :> {y, -x}, "\n");

  (*  same as  *)
ReplaceAll({{5,3}, {6,2}, {7,1}}, RuleDelayed({x_, y_}, {y, -x}))