C / C++ / MFC

HFONT hCurrFont, hNewFont;
LOGFONT lf;

// 1. Get the button's current font.
hCurrFont = (HFONT) SendDlgItemMessage ( hMyDlg, IDC_MY_BUTTON, WM_GETFONT, 0, 0 );
GetObject ( hCurrFont, sizeof(LOGFONT), &lf );

// 2. Change the font however you want by tweaking the LOGFONT members.
lf.lfWeight = FW_BOLD;

// 3. Create a new font.  Note that in "real" code, you should save this HFONT somewhere and delete the font when the dialog closes.
hNewFont = CreateFontIndirect ( &lf );

// 4. Make the button use this new font.
SendDlgItemMessage ( hMyDlg, IDC_MY_BUTTON, WM_SETFONT, (WPARAM) hNewFont, TRUE );

// in main message-handling switch
  case WM_TRAYICONCALLBACK:  // or whatever you call your callback message
    {
    if ( MY_TRAY_ICON_ID == wParam &&
         <font color=red>WM_RBUTTONUP == lParam</font> )
      {
      // Now call TrackPopupMenu()
      }
    }
  break;