Skyvia does not support custom fields in the default Jira connector, and thus, this scenario cannot be implemented with the help of the Jira connector: https://skyvia.com/resources/docs/index.html?jira_connections.htm
However you can try to create a custom REST connection. We will prepare all the necessary data to create it for you (we will describe the type of authentication, prepare metadata with custom fields). After that, based on this data, you will need to create a REST connection in Skyvia and use it in your package. If such an option suits you, please send us the following information:
- specify tables and API names of custom fields;
- fields data types (with maximum length if it's a string);
- an example of your data.
As for objects added by a plugin, it is not possible to support such objects.