Updating an add-on

If I create an Add-on and start deploying it in projects, but then realise I want to add functionality to the Add-on how can I do so without just replacing the entire add-on in the dropin folder of the Capella file structure and losing all of the project information because that viewpoint no longer exists. Is there a way to update add-ons without losing project data?

It depends on the changes you intend to do afterwards and the goal of your addon.

If your addon doesn’t enrich the capella concepts or diagrams but add new functionalities (import / export, command lines, webservices, etc etc) then any changes on your addon structure shall not have impacts.

If your addon contribute to capella concepts or diagrams, (by adding a viewpoint adding elements in the capella model or diagrams), then the user model (.aird / .capella) will have strong dependency to the addon structure, and you shall contribute to the migration process to migrate the user model to the newer version, otherwise the user may face to issues or have manual steps to use the new version of the addon (diagrams to be refresh manually to repair diagrams)
But anyhow, contributing to the migration to adapt user files to addon changes is something doable and we do it on each releases.

For instance,
we did large renaming on concepts in the 1.4.x

or renaming some images from PNG to SVG

or enable some new filters on diagrams