I understand that with append you mean combining the results of two views with identical schemas. This being the case I think that what you are looking for are [UNION views](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/creating_derived_views/creating_union_views/creating_union_views). I would read the documentation linked for more information about how this type of derived view works.
Regarding the second part of your question the only changes that you should worry about propagating are the changes on the actual source. In case something is changed on the schema of the underlying tables I just open the affected base views and under the Edit tab click on ‘[Source Refresh](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/creating_data_sources_and_base_views/source_refresh/source_refresh)’. This will take care of propagating these changes to the affected derived views if you choose to on the popup window.
Hope this helps!