Yes it is possible. If you cant do it in the editor, you can extract a .txt file from the .mpq, edit it and import it into your map.
Can't remember the name of the file. If anyone haven't told you a solution, then I will when I come home.
UPDATE:
I found the .txt file in the .mpq. Open it at finde the rally point command, and change the text.
Then import it into your map with the path: Units\CommandStrings.txt
{EDIT}
Somehow I cant upload the file to my preview post:S