Is it possible to create a scan that would look for any stocks making 400 day closing highs, but at the same time include stocks making new closing highs that don't have 400 days of data?

Thanks

It isn't possible using a formula, but it is possible.

Add a 1-period simple moving averge to price. Then click on the moving average and select Create Condition. You will want to set the Condition drop-down to New High set to At 400 Bar High.