Unfortunately, you can't lock a deal property based on a trigger like a stage change or contract status in HubSpot.
What you can do (on Professional or Enterprise plans) is restrict editing access to certain deal stages — so only specific users or teams can edit deals in those stages. But this doesn’t apply to individual properties, and it’s not dynamic at the property level.
A common workaround is using workflows to revert changes or notify admins if a "locked" property is edited after a certain stage.
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To solve this issue, we need to follow a few preliminary steps:
Create backup properties: In this case, you’ll need to create backup properties that will store the original values. These values should be copied using a workflow triggered when a deal enters a specific stage. The workflow should copy the value from the original property into the corresponding backup property.
For added security, you can restrict access to the backup properties in their configuration settings.
Restore the original value if it changes: Set up a second workflow that triggers whenever someone changes the original property. This workflow should restore the original value from the backup property. Additionally, you can add an action to send a notification to an admin or another responsible person.
Let me know if you'd like help setting up these workflows or if this approach meets your requirements.