Including a constant Poisson contribution via isocurvature in CLASS

[patricio-c]

Hi, I would like to generate a matter power spectrum in CLASS that includes a constant Poisson contribution, using an isocurvature perturbation mode, and evaluate it at a given redshift.

As a simple illustration, I am attaching a figure where the Poisson term was manually added to a CAMB power spectrum. I would like to implement this contribution directly within CLASS instead of adding it by hand.

Is there a recommended way to define such an isocurvature component in the CLASS input parameters, or any example configuration that I could use as a reference?

Thank you in advance for your help.