VB.net Append text in the end of txt file

[luckydead]

Hello, can someone advice me how i can make correct to add new value string in text file at specific location.
I will give full example

So let's start i have a file File1.txt
Inside i have this information:

Line1: /grant Username2OI)(CI)F /T
Line2: /GRANT:Username2,Full /UNLIMITED

so what i want to do programatically, in Line 1 i want to add after /T new record string
example result will be:

/grant Username2:(OI)(CI)F /T /grant Username3:(OI)(CI)F /T
then for line 2 i want to add before the /UNLIMITED new string
example result will be:
/GRANT:Username2,Full /GRANT:Username3,Full /UNLIMITED

how i can make it like that? - Please note Username are just example text it can be other text
And for example how can i add new line in the end with string after line2, to add new strings each line if i need?

[jmcilhinney]

Your title says:

Append text in the end of txt file

but your post says:

add new value string in text file at specific location

It would be helpful if your post didn't contradict your thread title.

[jmcilhinney]

You can't really insert text into a file at an arbitrary point. You need to read the file, process the data as appropriate, then write all the data back to the file. You can call File.ReadAllLines to read the file into a String array. You can then modify any element of the returned array however you want; each one is just a String. You can then call File.WriteAllLines to write the array back to the file.

If you want to add new lines at the same time, you can create a new List(Of String) and populate that from the array. You can then add, edit and remove lines as desired before passing the List to WriteAllLines.

Before you ask, no I won't provide an "example", which really means write your code for you. I'm prepared to help further but I would expect to see an attempt to implement the advice already provided first.