let's say I send eth to a second address but give a low commission so I don't overpay.
Then I go to work but as soon as the transaction arrives at the destination address I want it to be immediately exchanged for USDT.
Can I set this up on 1inch / uniswap?
You will pay a commission for transferring coins to another address.
You will pay the commission for the smart contract at the second address.
You will pay commission for smart contract on 1inch/uniswap.
But you can make it much easier if you install the 1inch/uniswap app on your mobile phone and exchange coins in a few seconds.
If you want the first option, then look for programmers.