Alternatively, you could wait for some coinbase outputs to mature and acquire a UTXO that descends from a coinbase output that only exists in one chaintip.

Thank you I had never thought of this...

Once you have any UTXO that only exists on any one chain, you can use it to split all of your funds by spending that UTXO along with others from your wallet.

This is complicated (!) but good to know... thank you for your response.