Add and move to the end of a string

Hi,

   Maybe this is a stupid question but i have a mental cloud , The problems is:

   I have a text box with a predefined text or not, what i need is to add a text to the text box and move the cursor to the end of this text box to let the user type the rest.

   txtboz1 = "1234567"

   I want to add 8901234 if the user press the key "/" keyascii 47 and let the user put any other text at the end of this one .

  I was trying with the sendkeys command but when i send the text and the "{END}" all the text becomes selected and the cursor is not at the end of the text box.

Any idea?
Thanks a lot