If you create NEM wallet and append address in your text, it doesn't create any vulnerability. It's just additional technical possibility. You can use it or not to use.

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My mistake - NEM has maximum 64 keys:
https://docs.nem.io/en/nanowallet/multisignature-multiuser

And NEM's fork "Symbol" has 25, but in 3 hierarchical levels:
https://docs.symbolplatform.com/concepts/multisig-account.html

As I understood, their wallets can work directly in browser.
https://github.com/NemProject/NanoWallet/releases
https://github.com/symbol/desktop-wallet/releases
Download universal zip archive - unpack - open index.html

(And BTW - they both can also save short messages)