Service Bridge Advanced Transform Maps - How to change nothing?

[tommccloud]

There is a requirement whereby an advanced transform map is required, I have a few questions as the documentation isn't clear about several things.

1. When the Configuration Item field is set on an Incident record for the Consumer, this will be sent to the Provider instance, the Provider instance will try and find a named match for the Configuration Item and then set it in the Provider instance. If this doesn't match, the requirement is to leave the Configuration Item as is in the Provider instance, but also post a work note to notify that the Configuration Item has been changed in the consumer and not mapped in the Provider. If I explicitly say to not set the output object when there isn't a match, then the comment: The following fields were updated by consumer XXX: Configuration Item: undefined. Is the approach to this to just use scratchpads to send across the information, check against the record and handle insertion etc.?
2. Is there a single piece of documentation that explicitly describes how to use the scratchpads? I've got it working between instances, but it feels messy, and I'd like to reference something that already exists. 
3. For only Change remote task definitions, I receive the error of "Unable to update field. Parent task missing." - I've offboarded/onboarded, recreated the Remote Task definition and it is only Change Request that is suffering with this issue. Is there any definitive troubleshooting? The parent field is populated and can be read. Providers can update the Consumer Change, the Consumer can not update the Provider.