EDI Webpad is limited to only allow simple configuration. To use all the features you need to utilize the API directly.
The following settings are available:
All data elements with alpha (A) or alphanumeric (AN) data types are validated against a syntax set of allowed characters. The default syntax set varies between standards and is either inferred from the file contents (EDIFACT would look into the UNB segment) or is statically set (X12 to use the Extended syntax set by default). This value overrides any existing sets and needs to list out every symbol/character, URL-encoded, which is allowed, without any spaces/delimiters between the characters.
More information for EDIFACT files validation
The identifier of the model to be used when translating EDI transactions to JSON. By default, the API will identify the model from the contents of the file and will try to load a corresponding model automatically. This value overrides this logic and used the specified model instead.