Thanks for point that out. Fixed.

It switches usernames immediately, but the last username still shows up when a link without a username is loaded.

This isn't a problem for me since I'll always be including a username, but I thought I'd mention it.

Np. Try now.

Thanks for getting to this so quickly!

Unfortunately, it seems a little buggy, as if the page is being cached or something. I'll open a link with username=creator3 and then different computers all have creator3 prefilled when they load the page. And it doesn't change to creator4 if I switch to username=creator4 (until the cached page expires?). I understand if you don't want to make big changes for this feature, but maybe a client side solution would be easier.

Thanks again