Assuming you have 1 BTC

You send 0.6 BTC to Address B. Your change 0.4 BTC will be sent back to change address (address C) in your wallet.

If you spend the coins or part of the coins you sent to address B and increase the fee in a way that it can make two transactions to be confirmed, because of that, miners will include your transaction into a block and it would be confirmed after the block is mined.

Instead of using 0.6 BTC or part of the 0.6 BTC in address B, you can use 0.4 BTC or part of the 0.4 BTC in address C to achieve the same result. It is called child-pay-for-patent.

I do not know much about BRC20 for now. But if possible that you are spending bitcoin and the transaction have change address UTXO (I mean a change back on your wallet), you can use part of the change address UTXO to create another transaction in a way that would be enough to make two transactions confirmed at a time. Your initial transaction is the parent while the new transaction is the child transaction.

Mempool is at 200 sat/vbytes. For the child transaction, you can set it to 400 sat/vbyte.

You not not use 50 sat to create transaction. At least, you will use around 111 sat which is 1 sat/vbyte, but the mempool is not accept such low fee now. Check the fee you used very well, it can not be that low.

Wallets that do not support opt-in RBF use to flag the transaction made on the wallet not to support RBF.