I created a Mathematics StackExchange account today. Unfortunately, before this, I posted a question as a guest (unregistered user). As my browser blocks cookies, I have lost access to this account. I have followed the instructions given on the relevant help center page, and hopefully, I will soon receive a response. In the meantime, however, the question has been answered. Is it somehow possible for me to accept an answer?
It's commendable that you want to accept an answer, but there is no rush. Even under normal circumstances, it is perfectly normal to wait a few days before accepting an answer. (There is such a thing as accepting too quickly.) And many answered questions remain without an accepted answer forever, which isn't ideal but is not a big deal, either.
If a Stack Exchange employee merges your accounts, great; otherwise, just move on.