Answer to if they can be added: Yes! they can be added. It's possible.
Couple of days back you asked this question:
http://www.codeproject.com/Questions/93963/How-to-Validate-a-Textbox-inside-the-DataGridView-.aspx[
^]
Regular expression looked like the solution that was acceptable to you, but then you were unable to form a regular expression that suits you.
Now, though after providing
full details on regular expression[
^], you are back to masked textbox.
Try and be sure of what you need to do. Don't just hit and try.