That would triggering hundreds of thousands of email notifications so I'm not sure it's a good idea...

Indeed, too much hassle when the workaround is very simple.

I assume the Bugzilla banner doesn't take dynamic parameters, right?

Click <a href="https://bugzilla.wikimedia.org/show_bug.cgi?id=NNNNN>here</a> to land in the corresponding Phabricator task.

Where NNNNN would be the bug number of the page you are seeing.

If this doesn't work, we could still add the static instructions in this banner, which appears in all Bugzilla pages:

In order to check the Phabricator task corresponding to this bug, just remove "old-" from the URL.

Whatever is the banner, we can document it in T366: Move Bugzilla to old-bugzilla.wikimedia.org. Closing as Declined here, because in any case we are not going to update all Bugzilla reports during the migration.

In T934#16029, @Qgil wrote:

I assume the Bugzilla banner doesn't take dynamic parameters, right?

Nope. :(

In order to check the Phabricator task corresponding to this bug, just remove "old-" from the URL.

Whatever is the banner, we can document it in T366: Move Bugzilla to old-bugzilla.wikimedia.org.

That's now in T1234 after spliting the redirect parts into two tasks. I've updated the banner message drafted in that task to cover this aspect.