You can create a new workflow which is a copy of the "Assets Cloud Post-Processing" workflow. (Refer Auto Start Workflows)
This workflow can contain all the process steps which are custom to the business requirements.
For the native steps to the OTB "Asset Update Workflow", most of the process steps are not required to be modified as the Asset Compute service takes care of them.
However, you can view list of workflow process steps which are native here at Workflow Step Properties and co-relate with the Supported workflows of the Asset Workflow Migration tool.
Hope this helps!