Due to an expired certificate on our Workflow site it seems that we need to uninstall and reinstall the Workflow manager. https://social.technet.microsoft.com/Forums/en-US/d935d8df-9de1-4d7f-9937-6e811b24b472/sharepoint-2013-workflow-manager-now-has-expired-certificate?forum=sharepointadmin Nowhere though can I find anything about the impact of doing this. ie) does this remove any existing workflows? What if we have a custom Action in one of our Workflows? Also, I asked in a separate question - how do I tell which CU I have on my Workflow manager? Does this have any impact on any other Sharepoint services? I can see my build-number but don't have a resource that tells me which build-number matches which CU. Thank you,
It does not remove existing workflows as those are already in the workflow manager databases. You will re-use your existing databases when creating the new WFM farm. You should use
Copy-SPActivitiesToWorkflowService once you've bound WFM back to SharePoint.
We had to do the same thing in our company last week - with no errors. Just be sure to backup all Workflow Manager DataBases and then restore them.
For the Custom Activity I agree with Trevor.
For the Build Number, I already answered your second question HERE