inactSymbols = <||>;

Attributes[myInactiveQ] = {HoldFirst};
myInactiveQ[_] := False

Attributes[myInactive] = {HoldFirst};
myInactive[h_] := myInactive[h] = With[
   {s = Unique["inact" <> SymbolName@Unevaluated@h]},
   Attributes[s] = Complement[Attributes[h], {Protected, Locked}];
   MakeBoxes[s[args___], frm_] ^:= With[
     {b = MakeBoxes[Inactive[h][args], frm]},
     InterpretationBox[b, s[args]]
     ];
   AppendTo[inactSymbols, s -> h];
   MakeBoxes[s, frm_] ^:= MakeBoxes[myInactive[h], frm];
   myInactiveQ[s] ^= True;
   s
   ]
myInactive[s_?myInactiveQ] := s
myInactive[s : List | Rule] := s

Attributes[myInactivate] = {HoldFirst};
myInactivate[expr_] := Replace[
  Unevaluated@expr,
  {
   i : HoldPattern[myInactive[h_][args___]] :> i,
   h_Symbol[args___] :> With[
     {in = myInactive[h]},
     in[args] /; True
     ]
   },
  All
  ]

myActivate[expr_] := expr /. inactSymbols

a = 1;
myInactivate[a = 2]
(* myInactive[Set][a, 2] *)

myActivate[%]
(* 2 *)

myInactivate[Sum[f[a = 2, z], {n, 1, 2}]]

myInactivate[Sum[f[a = 2, z], {n, 1, 2}]] //
 Cases[#, _?myInactiveQ, All, Heads -> True] &
(* {myInactive[Sum], myInactive[f], myInactive[Set]} *)

myInactive[Set][a, 2]