> For the complete documentation index, see [llms.txt](https://doc.wearepatchworks.com/product-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.wearepatchworks.com/product-documentation/virtual-environments/implementing-virtual-environments/configuring-a-virtual-environment-version/configuring-virtual-environment-replacements/replacement-scripts.md).
# Replacement scripts
## Introduction
Having [chosen to configure script replacements for a virtual environment](/product-documentation/virtual-environments/implementing-virtual-environments/configuring-a-virtual-environment-version/configuring-virtual-environment-replacements.md#configuring-replacements-for-a-virtual-environment-version), a new replacement rule is displayed, ready for you to configure:
Having defined the first rule, you can add more - you must create one replacement rule for every [script](/product-documentation/developer-hub/custom-scripting.md) that you need to replace in every process flow that will run in this environment.
## Defining replacement rules for a script
{% stepper %}
{% step %}
**Select the required ORIGINAL script**
Use the `original` dropdown list to select the first script in a 'master' process flow that must be replaced when this process flow runs in the given virtual environment - for example:
{% hint style="info" %}
As you work through your replacement configuration, it's helpful to view related ['master' process flows](/product-documentation/virtual-environments/implementing-virtual-environments/creating-a-master-process-flow.md) in another browser tab. You can duplicate a Patchworks browser tab and navigate to a different page whenever needed.
{% endhint %}
{% endstep %}
{% step %}
**Select the required ORIGINAL script version**
Move down to the field below and choose which version of the selected script to apply - for example:
{% endstep %}
{% step %}
**Select the required REPLACEMENT script**
Use the `replacement` dropdown list to select the replacement script that must be used when this process flow runs in the given virtual environment - for example:
{% endstep %}
{% step %}
**Select the required REPLACEMENT script version**
Move down to the field below and choose which version of the selected script to apply - for example:
{% endstep %}
{% step %}
**Confirm your selections**
Click the `create` button (associated with this replacement rule) to confirm your selections:
The rule is added:
{% hint style="info" %}
Once a rule is confirmed, it can't be edited. If you need to change a replacement rule, use the 'trash' icon to remove it and add a new one.
{% endhint %}
{% endstep %}
{% step %}
**Add more replacement rules for scripts**
To add another replacement rule for a script, click the top-right `create` button:
Update the new rule as required, then click the associated `create` button to confirm your selections:
Repeat as many times as needed to define all required script replacements for all process flows that will be running in this virtual environment.
{% hint style="info" %}
If you don't want to define ALL script lookup replacements now, that's OK. For example, you might choose to add the minimum number of replacements needed for [testing](/product-documentation/virtual-environments/implementing-virtual-environments/testing-a-process-flow-against-a-virtual-environment.md), then define remaining rules (in a [new draft](/product-documentation/virtual-environments/implementing-virtual-environments/configuring-a-virtual-environment-version/understanding-virtual-environment-versions.md)) later, after initial testing is complete.
{% endhint %}
{% endstep %}
{% endstepper %}