Message:Today is 27th of June 2022. This address is owned by edgycorner.
Signature:HIVJozDmMMtjnAKGUhcjT98OLIOcwUQZhSiVV05Rp2gQPl314TqwHTqcOWwonLlBZSNMgvVG18M/Us89vHUvKrE=
Simply stated, there is no issue with signing with the 1SiD... address, but if somebody signs with the 1edgy... address, we should believe them over anything that you say. That's how signature proofs work.
Typically, if you want to use a different address, you would sign a message with the original address saying so. Then there is no question, even if the original address is compromised.
Signing the address initially is not strictly necessary. It's a good idea in order to make sure that you can sign a message with the address, but it is really just a formality. The reason is that there is no benefit to claiming that you own a random address. You don't really need to prove that you own an address until you want to make a statement that requires a proof. In this case, the purpose of posting an address is to be able to prove that you are the original owner of the account at some time in the future.