This came up in another thread, and thought it could be reposted here (slightly reworded).
I strongly advise against modifying the AUT through testing. If you modify the AUT, any test you make is no longer testing the AUT. You are testing something else entirely.
If the user can’t do it, through normal page interactions, your test should not do it, either .
You should strive to test what is there, not modify it so you can test something else instead.If you believe the page is behaving improperly, tell the developers.
If you believe the page is untestable, tell the developers.
If you believe the developers could modify the page to aid testing, ask them to do that.
If you modify the page, your results (passes and failures) are meaningless.