Here's way along the lines in the OP:

Manipulate[
 With[{opts = Sequence @@ opts},
  Plot[Sin[x], {x, 0, Pi}, opts]], {p, 
  PopupMenu[Dynamic[p, (q = opts[[#, -1]]; p = #) &],
    Thread[Range@Length@# -> #] &[First /@ Options[Plot]]] &},
 {{q, Null},
  InputField[
    Dynamic[q, (opts = ReplacePart[opts, {p, -1} -> #]; q = #) &]] &},
 {opts, None},
 TrackedSymbols :> {opts}, Initialization :> (opts = Options[Plot])]

Here's way along the lines in the OP:

Manipulate[
 With[{opts = Sequence @@ opts},
  Plot[Sin[x], {x, 0, Pi}, opts]], {p, 
  PopupMenu[Dynamic[p, (q = opts[[#, -1]]; p = #) &],
    Thread[Range@Length@# -> #] &[First /@ Options[Plot]]] &},
 {{q, Null},
  InputField[
    Dynamic[q, (opts = ReplacePart[opts, {p, -1} -> #]; q = #) &]] &},
 {opts, None},
 TrackedSymbols :> {opts}, Initialization :> (opts = Options[Plot])