Ok so just in case anyone else finds this, i had to create an entirely new version of this custom action using the AWS CLI - I used the JSON template in the AWS CodePipeLine user guide and amended using the old values (luckily I had still got the custom action fields from the original in my terminal buffer):
"description": "The name of the build project must be provided when this action is added to the pipeline.",
$ aws codepipeline create-custom-action-type --cli-input-json file://jenkins_provider.json
....but I still can't add this now using the browser method, it just try to use Version 1 all the time and errors which is really annoying, don't suppose anyone knows a fix other than contacting AWS? you live and learn huh! (it is just for study purposes this project using my account).
You are right that if custom action is updated via web-console version field is missed. Possible workarounds are to use API/CLI as you've done or create an action with the new name.
Thanks for bringing this to our attention! I don't have any ETA, but this issue is added to our backlog.
- CodePipeline does not use 'Server URL' parameter of custom action to communicate with Jenkins. So even if instance's IP has changed Jenkins will be able to poll CodePipeline for jobs (but URL to the job in the CodePipeline web-console will be broken).
- You can look at CodeBuild service  for your unit/integration tests to avoid having dedicated Jenkins instance all the time.
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