It’s your own fault for buying code blueprints; You should be very well aware of the risk.
The blueprint system is designed to provide people with very low understanding of programming paradigms… to develop programmable systems.
It’s acceptable that the great majority of blueprint systems published are made by people that don’t really understand what they’re doing, because they have close to no previous experience designing tools to be used by third-party developers.
There are many many many mistakes (many) I’ve seen in blueprint code that are published to the Marketplace; Most of the time the author is using a “Unity developer mindset” to build the systems and ignore many of the possible compatibility with Unreal Engine’s internal systems itself. That may work for the project the blueprint is designed into, but once you implement the thing inside a real game project then everything starts to fall apart.
There’s only a few I’ve seen doing a really great job (because those authors are actually good programmers).
But, well, no; You cannot rework someone else’s “Advanced XX System” and republish it even if you’ve made it work properly.