Over the pass few years much has changed for data structures within Appian, specifically with record types and custom data types (CDT). There does not seem to be any official documentation on how to convert an application designed using CDTs to one using records. While CDTs have not been entirely fazed out but rather relegated to support with plugins and smart services, it is often more performant and (based on Appian documentation) preferred to build using record types.
My questions are:
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1. Yes, but depends on the use case.
2. No, this is lots of manual labor.
IMHO there is no urgent need to convert existing apps to records as Appian will support CDTs and datastores for the foreseeable future. When modifying an app, I suggest to refactor existing things towards records when touching them.