The meta tag in the page are not modified, but AdManagement will use those values.
pbstck_context:xxxx
You can see the current page context in AdManagement’s logs.
To have access to our logs, you can use localStorage.kleanads="debug"
And that, using the URL, we are overriding certain values.
ad:xxx
You can see within the ad call's payload (GAM call) cust_params the new values retrieved from the URL. Those key values are sent at page level targeting.