inserting a clip file just inserts a collection of nodes (the clip) into your node network, but it does not connect these new nodes with the network automatically. You need to connect them manually.
For example, the sunset II pack comes with clip files, which contain a new atmoshpere group and lighting group.
If you insert them to your existing project, you need to connect the last cloud layer shader from the clip file to the atmosphere input of your planet shader (thereby effectively disabling your original atmosphere, because it's no longer connected) . Then you need to disable the original enviro light and sunlight nodes.
In order to use the NWDA presets it's important to understand some fundamentals of how the node network and how everything connects and what the different node types are. Usually with our packs come not only clip files, but also tgd files (complete projects) where you can see by example how you need to connect things.
I'd be glad to help you out as well with specific questions on NWDA presets. Just send an email to webmaster {a t } nwdanet {dot} com if you need us.
Cheers,
Frank