Can I set a parameter as part of the run?

Build Environment
1

In Circleci version 2.1 I would like to create a parameter, then set a value to the parameter during the run.

Something like:

parameters:
  my-param:
    type: string
    default: ""

jobs:
  build:
    steps:
    - checkout
    - run:
        name: Set the param
        command: << parameters.my-param >> = my-value

The reason for this is I am running a command that determines the value of the parameter, and I do not know if ahead of time.

Is this possible?