The Bitcoin blockchain doesn't know what your setup is until it receives a transaction. So when you send a single sig transaction for the first time that is when the seed is recorded on chain and finally in use. Initializing a wallet is only a local event to you.

I use a passport which uses a lot of the same software as coldcard and I can say for sure that I can have two wallets with the same seed on one device. However mine are one with a passphrase and one without. I would expect the same functionality to be available for multisig though.

If you're worried it will overwrite your single sig on the device just make sure you have your seed phrase handy so you can recover it. Maybe someone else can answer definitively that coldcare supports multiple wallets so you don't have to go through the hassle of recovery.