No indeed you need to change the keypair used by your node, potentialy in its own profile (--mdb profilename) to avoid tampering with your main Duniter profile. Your node needs to have a keypair associated with one of the members, otherwise you can’t forge a valid block (since your not a member).
To generate signatures you can indeed try to use our Rust implementation which is unit tested to give valid results with the main implementation. Without this code, all you have to do is sign the complete document (in text format while respecting line breaks) with your private key with any ed25519 cryptographic library.