How to enable "Replace object" option and "Pick object" action for plugins

Hi there,

I'm developing a custom plugin and I would like to achieve:

1. To have the "Replace" feature enabled; but I can't find anything about it.

When I try to use the "Replace object" I get a message that says: "There are no objects in the selection that can be replaced".

2. Be able to choose an object in an action with my plugin but there are no objects when trying to pick one.

Any help, ideas or examples would be much appreciated.