How can I load datapacks only in individual worlds instead of all of them?

I have created two small datapacks that increase the build limit in the End and the Nether. I have the standard worlds on my server (world, world_nether, world_the_end) but also custom worlds. One of them is an End dimension and the other a Nether dimension. I want the build height to be increased only for my custom worlds, not for my vanilla worlds. Is this possible and what do I have to do?