Hi Oscar,
this code example shown below from my grid class part of Init event . it removes at runtime all textboxes from the grid and adding my own textbox class to all columns.

* grid init event
FOR EACH oColumn IN this.Columns
   WITH oColumn
      .RemoveObject('Text1')
      .NewObject('text1','GrdAddNew',this.ClassLibrary) &&grdaddnew my textbox class name
     .CurrentControl='Text1'
     .text1.visible=.t. 
     ENDWITH
ENDFOR

you can do this on your form and if you want you can apply this for some columns

eg. for grid init event

WITH this.Columns(4)
  .RemoveObject('Text1')
   .NewObject('text1','GrdAddNew',this.ClassLibrary) &&grdaddnew my textbox class name
    .CurrentControl='Text1'
    .text1.visible=.t. 
 ENDWITH

HTH