Synopsis:

• Though there is no built-in tooltip support for InstallScript or InstallScript MSI projects, the project can be customized by writing tooltip functionality as described in the official Microsoft documentation at this link:
  
  https://docs.microsoft.com/en-us/windows/win32/controls/create-a-tooltip-for-a-control

• Also, here is a link to a CodeProject sample which has already Edit control's tooltip function been implemented, see the Balloon Tips Section:
  
  https://www.codeproject.com/Articles/162933/Programming-User-Interface-in-InstallScript
  
  
• If the expectation is to add pretext to the edit control, like "Enter Text Here," this can be achieved by editing the custom or predefined dialog's function with the CtrlSetFont function.
  
  
• Sample CtrlSetFont function InstallScript code is here.