If it falls within fund's target they should just buy it, without thinking. That's the point of low cost ETFs. There's even a known arbitrage opportunity with

If it falls within fund's target they should just buy it, without thinking. That's the point of low cost ETFs. There's even a known arbitrage opportunity with things like S&P500. When the S&P committee decides to include a new stock (and delist some other stock) you can front-run the purchases by the giants like SPY or VOO, slightly inflating the stock's value just when the ETFs buy it from you.