If that's a security risk then it already exists.
the edit box already works, it just breaks after 256 characters. If the limit was extended to 1024 characters then this does not open up any attack vectors which did not already exist. (it already scrubs the input, only alphanumeric characters get parsed, all others get erased)
Or if SC2 was able to read a plain text file character by character instead of through using the key/section xml reader it currently does. If there is the possibility to make it overflow and corrupt further data or inject code into the code section of memory then this capability would already exist in the current form through banks.
There's no way to read in text which the game will excecute as code, but if there were then that means that anything it could exploit could already be exploited by a malicous map maker making a map which has a virus in it.