Your rule set (2.2.9) is "bit" old, you should use a newer version (actually 3.3).
I don't understand your question exactly "what can be done if I inject...".
As you can see, the operator is the @rx, and it has an argument. The list of variables contains the ARGS, so I guess your form contains an input field, what will evaluated as an ...
There are several methods to achieve this.
The oldest and simplest approach is called Code Caves. Simply put, the process memory has some allocated, but unused memory. By modifying the code - either by injecting it dynamically or overwriting the binary file - code can be inserted into the code cave and be jumped to and returned from.
The advantage ...
The script is collecting your IP Address and subscriber ID as well: Open this link and check your Subscriber ID and IP Address as well.
Since BSNL did not comply with users' complaints on HTTP Ad Script Injection I have reported a local solution (with the help of Adguard)
What this would do?
Remove Click-jacking Ads on HTTP sites
You don't specify which host o.s. you're on, so I'll assume Linux. You might stat the files and directories before the compromise occurs, to see if there are any differences afterwards?
# %i inode number
# %s size in bytes
# %b count blocks
# %B block sz
# %Y time of last data modification, seconds since Epoch
# %Z time of last status change, seconds ...