That's because you currently use the scriptfile itself to store your lines - of course the file changes if you writeini/remini to it, and mIRC, monitoring changes to the scriptfile, hence asks you time and again what to do.
If you really want to stick with an apparently flawed script, replace the location " $+ $script $+ " with another file - for example $qt($scriptdirmas.ini) as suggested above. Also make sure there's no other command in that $script modifying the scriptfile itself (that is, change all other references to $script by the same token).