Without more details about how you interact with OpenNMS, it's hard to say what would be the best approach to achieve your ultimate goal. I can say, however, that trying to have "different types" of nodeDown events sounds like the wrong approach. You could probably do it, but you would be in for a long struggle against the design of the poller.
If you don't care at all about the up/down status of the laptops, you can just tell the poller to exclude them from its normal operations. A great way to do this is with a surveillance category used in the filter expression of a poller package. For example, you might put all the nodes whose up/down state you do care about into a category called Track_Uptime. Assuming you're using the default version of poller-configuration.xml you might then change the example1 package like so:
(That's not a typo, there's really no space between "catinc" and the category name. The syntax is a bit unwieldy.)
Because of a known bug in 20.0.1, you'll probably need to restart for this change to take effect. Now only services on nodes belonging to that category will be monitored for up/down state by the services defined in that package. Other nodes can go up and down all they want and the poller will say nothing about it.
I realize this may go too far in the opposite direction for your liking. OpenNMS is flexible enough that a million different in-between solutions are achievable; the above is just one possibility that lends itself to concise summary. I hope it's helpful.