in the OOTB libraries from Post Configurator is a standard implementation to support chains during postprocess. To get the correct positions it's necessary to define kinematic informations in the post about the chains, if they are different to the default configuration of postprocessor, e.g. spindle axis or axis vector of 4th/5th axis.
The post calculate the correct positions now, depending on the mom_kin-variables which belongs to the chain.
There are 2 ways to create chains. Automatically from the MTB-Model, but then maybe Heads are not included if they are dynamic devices. It's also possible to add chains per Tcl commands and mapping chain conditions in the UI of Post Configurator. For further information how to handle the chains please take a look in the attached material.
When a chain is switching during postrun or is active in beginning of postprocess, the MOM_reload_kinematics command is used, so this reload e.g. the variables which are defined in the UI of Post Configurator and all the others from default chain. I know that we also use the MOM_reload_iks_parameters in some cases and this is implemeted in the generic command for calculation of 4th and 5th axis points.
In the sim17 sample the most of tcl-implementation belongs to logic of toolchange and which chain is active, dependent to the active device (proc LIB_SPF_define_active_chain_custom). For CSE we have defined some rules that simulation works fine, which are described in the document you mentioned.
Hope this helps and give a few more understanding of the Multichain feature.