Crengine font weight value

[foreverconfused]

Hello,
I apologize if this is not the best place to post this.

So, I am using an epub reader app called LxReader, which is also based on crengine.
Just like KOReader, you can change font weights. However, the issue is that this value is enforced on ALL fonts: Sans, Serif, Monospace, etc.

I was looking for a way to edit the source code of the app to separate this value into 5 different font types recognized by the app (Serif, Sans, Cursive, Fantasy, and Monospace).
Essentially, each slider would affect its own font type.
I even attempted to do this with AI, which was successful in everything up to this point.

Can you tell me if this is even feasible on crengine, or does it just force the same font weight on everything with no way to change it?

I really appreciate your input on this matter.
If this is indeed feasible, please tell me what I should target so I can make another attempt.

Thanks in advance.