[
    {
        "ParameterKey": "XYZ",
        "ParameterValue": "{someval}{index}"
    },
    {
        "ParameterKey": "ABC",
        "ParameterValue": "staticval-{suffix}"
    }
]

#! /bin/bash

# create output file from template
cp templates/parameters.json.template generated/parameters.json

# merge dynamic values into templated file
sed -i "s/{someval}/$SOME_VAL/g" generated/parameters.json
sed -i "s/{index}/$INDEX/g" generated/parameters.json
sed -i "s/{suffix}/$SUFFIX/g" generated/parameters.json

aws cloudformation create-stack ... --parameters generated/parameters.json ...