type
  TControlAccess = class(TControl)
  end;

procedure TFormMain.FormCreate(Sender: TObject);
var
  I: Integer;
begin
  for I := 0 to ComponentCount - 1 do
    TControlAccess(Components[I]).OnMouseEnter := CustomGenericMouseEnter;
end;

uses
  ..., TypInfo;

procedure TFormMain.FormCreate(Sender: TObject);
var
  I: Integer;
  Comp: TComponent;
  Prop: PPropInfo;
  M: TMethod;
begin
  TNotifyEvent(M) := CustomGenericMouseEnter;
  for I := 0 to ComponentCount - 1 do
  begin
    Comp := Components[I];
    Prop := GetPropInfo(Comp, 'OnMouseEnter', [tkMethod]);
    if Prop <> nil then
      SetMethodProp(Comp, Prop, M);
  end;
end;

uses
  ..., System.Rtti;

procedure TFormMain.FormCreate(Sender: TObject);
var
  I: Integer;
  Ctx: TRttiContext;
  Comp: TComponent;
  Prop: TRttiProperty;
  V: TValue;
begin
  V := TValue.From<TNotifyEvent>(CustomGenericMouseEnter);
  for I := 0 to ComponentCount - 1 do
  begin
    Comp := Components[I];
    Ctx.GetType(Comp.ClassType).GetProperty('OnMouseEnter');
    if (Prop <> nil) and (Prop.Visibility in [TMemberVisibility.mvPublic, TMemberVisibility.mvPublished]) then
      Prop.SetValue(Comp, V);
  end;
end;