Can you plant a Cordyline in a pot in the ground to stop it getting taller?

I suspect it wouldn't be all that happy in a pot longterm. They don't cast a lot of shade once taller but if you really need to keep it to that height I wonder if a coloured phormium might suit you better for a spiky-leaved effect. There are some cultivars which are dwarfing compared to the 8ft high ones. Red Star isn't supposed to grow all that tall anyway compared with the green ones, but what nurseries say tends to vary a bit. Mine must be about 1.5 tall and grows only slowly in the shallow soil but my parents one, planted in much better ground is about 2m by now.

It's more likely to stay smaller if kept in a pot, but maybe you'll just have to replace it with another one when it is too big.