I did try enabling/disabling "Use NiOverride" and the give spell. No effect with that, either. My PC has a base UUNP body but did have values added through other inflation mods (SGO and MME with SLIF).
Just to be sure, I added some sliders to my character (set Big Butt and Breasts SSH to 2 in Racemenu) and tried the give spell. That, unfortunately, did not work either.
*Edit: Upon further testing, I still have not resolved the issue, but I found that I am successfully absorbing the simple node NPC GenitalsBase which was one of the nodes listed in my .json. It's the only simple node that I have added, and it appears to be the only one that did anything. These nodes have not yet worked (but I'm still trying to figure stuff out): BreastsSH, BreastsSSH, BigButt, AppleCheeks, Thighs, CalfSize, PregnancyBelly, Hips, BigTorso, ChubbyLegs, Legs, DoubleMelon.
*Edit #2: I think I've got it figured out. Using NiOverride, you can only edit nodes that are available to the body, not Racemenu sliders afaik. I made a new .json file that works because it only utilizes nodes (I've attached it just in case anyone else has my problem). I then use Sexlab Inflation Framework to adjust NiOverride to correspond to different changes in Racemenu's sliders for my body type. Luckily, this means it's not a problem at all with SLDD--just with my understanding of how NiOverride works in tandem with this mod and SLIF.
Nice detective work! Glad it's working