Better Balanced Combat can be manually installed with a bit of effort.

I recommend you avoid reading the following and simply install it with Vortex or NMM (depreciated) but if you must then please continue.

Please read this whole article before continuing with manual install.

Here's what you need to know:

Folders
Main - Contains plugins for the main game
Morrowind Rebirth - Contains plugins for the Morrowind Rebirth Version (Don't use with Main Version)
Tamriel Rebuilt - Contains plugins for the Tamriel Rebuilt Patch (Requires Main Version)
Small Patches - Contains smaller single .esp patches
Optionals - Contains optional plugins that do various other effects
Auto Patcher - Contains the auto patcher files, move BBCAutoPatcher.pl and tes3cmd.exe (Windows)/tes3cmd (Linux) to your game Data Files directory along with the BBCAutoPatcher file located in the folder for your operating system. You can run the OS specific file from your Data Files directory to generate an auto patch. To run the patcher on Linux see this.

Subfolders
Complete - Complete version with all modules in one plugin
Modules - Folder for custom install. Must always have the base module, then you can pick what other modules you want to install.

Module descriptions:
Base: Need this to use the other plugins in the same Modules folder.
Effects: All the changes to effects (spells, enchantments, etc.) to make the game work better with 100% hit chance.
Extras: Speed boost, magicka/stamina regen, removal of annoying combat messages.
Weapon Stats: Changes to weapon range, speed, and damage to make them more enjoyable.

The Advanced Mode plugin enables skill effects in spellmaking and enchanting again. Better Balanced Combat disables them by default because weapon skill effects don't do anything to NPCs anymore with this mod, they do still work on self though. Just be aware of that if using the Advanced Mode plugin.

Normally you'll want to load BBC after all other mods. If you want to use a mod that edits vanilla creature types, races, spells, spell effects, enchantments, ingredients, potions, or weapons then BBC may overwrite some of it's changes. You can load these mods after BBC to keep all of their changes but I won't guarantee game balance if you do. If you load anything after BBC that edits vanilla races or creature types specifically then you must also use the included auto patcher. Don't load anything after the auto patch.

When it comes to load order of the BBC plugins you'll want to load the Main/Rebirth plugins first with patches following. Always load the base module before the accompanying modules when doing a custom install.