I have already post this idea of feature on the Community Requests for MCreator 1.9.2, but I will post it here also.
In the Mod Options, when we click on Esc, there is all mods installed, and when we click on them, there is a Configuration button. So, I would like to have an option into MCreator to add some a mod element or something else to add configuration options. I find some links to help you to implement this feature. I know that the first link can be a little bit outdated, but it can help you with the base.
Hoping that you will add this feature, and the links will help you !