you don't need to daisy chain PSoCs for that. Send your external UART command with ID to all PSoCs simultaneously by connecting all PSoCs UART Rx to same bus line, and let each PSoC to identify if this correct id or not. This way you need to implement only one same standard Rx protocol on each PSoC.
If you need to daisy chain because of wiring considerations that does not
really change solution approach. ISR would be preferred due to latency
considerations, but polling also an acceptable method depending on what
other CPU activity is required.
Of course daisy chain approach does not lend itself to a robust network
approach, given that one node goes down it takes out all nodes downstream.
If distances not too great a wireless net might be more appropriate, star, mesh....