GREP is very important to me, but I use a script that scans an entire book and applies custom kerning pairs in one pass. This honors the EULA that says no alteration of fonts, but it also allows me to make adjustments consistently and completely throughout large documents.
I have so many custom data sets for faces, and this is largely what distinguishes my work, so there's really no point in using an application if I can't use it to distinguish my work.
Here's a link to the script (and others). Maybe someone can comment on IF this type of scripting is accommodated, and if not, would this be something that would be included in future versions. https://creativepro.com/files/kahrel/indesign/kern.html