Been a while since I modded Skyrim so please forgive me, my knowledge may be a bit rusty.

The best way that worked for me is to create a custom .esp plugin through sseedit and place all the personalized patches there. SSEEdit should have the option to create an empty plugin, I believe.

If you want to edit Serana’s record, add said record to the plugin and make all the necessary changes, then save the plugin and place it in the bottom of the load order. If you use LOOT to automatically sort your load order, add a custom rule to your plugin so it will be in the bottom.

This is the general go-to procedure when manually patching mod conflicts. As for your specific case, there might be a parameter in Serana’s record which determines what model/textures she appears as. If that’s the case then you should be able to change it to what you need.

For mods affecting npc appearance it would be easier to move another mod that affects serana into a higher load priority because it’s likely the appearance mod is overwriting both in the plugins section and in the mod folders section of the textures and meshes due to headmesh generation and ect. So if you have mod 1 and mod 2 loaded in mod organizer 2 for example, and mod 2 makes serana furry and mod 1 is normal looking serana you want mod 1 to be below mod 2 in mod organizer 2 on both the left and right panel so that mod 1 has priority overwriting both.

Alternatively you can delete the serana npc section of mod 2 in sseedit and then delete the associated serana meshes and textures in the mod folders which will have the last few digits of seranas id as the file names.

If you use vortex I have no idea how to use it because I haven’t used it before and if you use Nexus mod manager, switch over to mod organizer 2.