LINQ doesn't let you add information to a Capture Action, that's because a Capture Action represents the original source, or beginning of an Information Supply Chain. Think of it as the initial action or activity which creates the first piece of Information needed to enable your business outcome. If you find yourself wanting to add information to a Capture node, that's a really good sign that there is more information and actions waiting to be discovered.
When you notice this situation, have a look at the Action and ask yourself: where do I get the information for this Action from? Keep going, and record the Information and Actions until you reach a customer or provider, they will be the original source, and that's where the capture actually happens. Changing the Capture node to an Action in the properties panel allows you to add and connect the extra elements you have discovered.
An external organisation can also be the original source of information coming into your organisation - that's when you use an Organisation node type.
Both examples are shown below: