If you want to target emission specifically, you can use an emission pass (activate in render passes) for this. It’ll give you an extra output on your render layer node, which you can then use to add bloom. For the rest you can use a separate glare node with a threshold adjusted to only show what you want effected.
Then add them together for the final image.
If that doesn’t work you can always do separate render layers for the different objects and composite them back together.
