Можно ли изменить вид текстового курсора edit'а или другого элемента управления?

Можно! В примере показано как создать два цветных "bitmap'а": "улыбчивый" и "хмурый" и присвоить их курсору edit'а. Для этого нужно перехватить оконную процедуру edit'а. Чтобы сделать это заменим адрес оконной процедуры Edit'а нашим собственным, а старую оконную процедуру будем вызывать по необходимости. Пример показывает "улыбчивый" курсор при наборе текста и "хмурый" при забое клавишей backspace.

unit caret1;

interface

{$IFDEF WIN32}
uses
        Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;
{$ELSE}
uses
        WinTypes, WinProcs, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, 
        StdCtrls;
{$ENDIF}

type
        TForm1 = class(TForm)
                Edit1: TEdit;
                procedure FormCreate(Sender: TObject);
                procedure FormDestroy(Sender: TObject);
        private
                {Private declarations}
        public
                {Public declarations}
                CaretBm : TBitmap;
                CaretBmBk : TBitmap;
                OldEditsWindowProc : Pointer;
end;

var
        Form1: TForm1;

implementation
{$R *.DFM}

type
{$IFDEF WIN32}
        WParameter = LongInt;
{$ELSE}
        WParameter = Word;
{$ENDIF}
        LParameter = LongInt;

{New windows procedure for the edit control}
function NewWindowProc(WindowHandle : hWnd; TheMessage : WParameter; ParamW : WParameter;
                        ParamL : LParameter) : LongInt
{$IFDEF WIN32} stdcall; {$ELSE} ; export; {$ENDIF}
begin
{Call the old edit controls windows procedure}
        NewWindowProc := CallWindowProc(Form1.OldEditsWindowProc, WindowHandle,
                        TheMessage, ParamW, ParamL);
        if TheMessage = WM_SETFOCUS then
        begin
                CreateCaret(WindowHandle, Form1.CaretBm.Handle, 0, 0);
                ShowCaret(WindowHandle);
        end;
        if TheMessage = WM_KILLFOCUS then
        begin
                HideCaret(WindowHandle);
                DestroyCaret;
        end;
        if TheMessage = WM_KEYDOWN then
        begin
                if ParamW = VK_BACK then
                        CreateCaret(WindowHandle, Form1.CaretBmBk.Handle, 0, 0)
                else
                        CreateCaret(WindowHandle, Form1.CaretBm.Handle, 0, 0);
                ShowCaret(WindowHandle);
        end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
{Create a smiling bitmap using the wingdings font}
        CaretBm := TBitmap.Create;
        CaretBm.Canvas.Font.Name := 'WingDings';
        CaretBm.Canvas.Font.Height := Edit1.Font.Height;
        CaretBm.Canvas.Font.Color := clWhite;
        CaretBm.Width := CaretBm.Canvas.TextWidth('J') + 2;
        CaretBm.Height := CaretBm.Canvas.TextHeight('J') + 2;
        CaretBm.Canvas.Brush.Color := clBlue;
        CaretBm.Canvas.FillRect(Rect(0, 0, CaretBm.Width, CaretBm.Height));
        CaretBm.Canvas.TextOut(1, 1, 'J');
{Create a frowming bitmap using the wingdings font}
        CaretBmBk := TBitmap.Create;
        CaretBmBk.Canvas.Font.Name := 'WingDings';
        CaretBmBk.Canvas.Font.Height := Edit1.Font.Height;
        CaretBmBk.Canvas.Font.Color := clWhite;
        CaretBmBk.Width := CaretBmBk.Canvas.TextWidth('L') + 2;
        CaretBmBk.Height := CaretBmBk.Canvas.TextHeight('L') + 2;
        CaretBmBk.Canvas.Brush.Color := clBlue;
        CaretBmBk.Canvas.FillRect(Rect(0,0, CaretBmBk.Width, CaretBmBk.Height));
        CaretBmBk.Canvas.TextOut(1, 1, 'L');
{Hook the edit controls window procedure}
        OldEditsWindowProc := Pointer(SetWindowLong(Edit1.Handle,GWL_WNDPROC, 
                                                                LongInt(@NewWindowProc)));
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
{Unhook the edit controls window procedure and clean up}
        SetWindowLong(Edit1.Handle,GWL_WNDPROC, LongInt(OldEditsWindowProc));
        CaretBm.Free;
        CaretBmBk.Free;
end;