Here's one way to do it:
Set Text [module1] to '11111111111'
Set Text [module1] to '{TXTSUBSTR:module1:0:2}5{TXTSUBSTR:module1:3:}'
Write '[Blue] {TXT:module1}' to log
{TXTSUBSTR:module1:0:2}
Returns the first two characters of your text variable(From position 0, which is the first character, and 2 characters long, so character position 0 and 1).
5
Is a literal character "5", which you could replace with a token if you need it to be variable
{TXTSUBSTR:module1:3:}
Returns the remaining characters of your text variable(from position 3, which is actually the fourth character position, to blank, or "Not Set", which means it'll keep going 'till it runs out of characters in your variable to return).