The code used in that post uses the ModbusMaster library which makes addressing individual devices straight forward.
If you look in post #51 in that thread you will find this
and with that the answer would be straight forward for any other slave ID.
However, since this is not an Arduino forum and hence has no affinity to the SimpleModbusMaster library you appear to be using it's beyond our scope to make it fit a library currently not Particle user seems to be using.