This change in fanfiction completely transforms the story's flow. Draco being part of the Golden Trio means that the typical Hogwarts house rivalries are put aside. His presence could introduce a different sense of humor as well. Slytherins often have a dry, sarcastic wit, which could contrast with the more straightforward humor of the original trio. Also, the power dynamics within the group shift. Hermione, for instance, might not be the only one with book smarts. Draco could also contribute in that area, leading to a more balanced group intellectually. This can open up a whole new world of adventures and challenges for them to face together.
It changes it a great deal. Firstly, the group dynamic becomes more complex. The Golden Trio was initially based on friendship and a common goal against Voldemort. With Draco in it, there could be more internal conflict at first as his background and beliefs are different. However, over time, it could add a new layer of depth. His family connections might provide different resources or insights that the original trio didn't have. And it can lead to some really unique storylines where they all have to learn to trust each other despite their differences.