installing mods mid playthrough?

[Dashin]

will the game mess up if i install a mod and then dont start over or can i just load up last save and it wont hurt anything

[ƒaylen §øl]

Depends on the mod to be honest. Mods that change textures are the most harmless so long as you either use a mod installer like NMM or backup whatever changes they make.

More complex mods can cause complex issues that effect all your saves.

It is always safer to start a new game when installing mods. Just read all the details about the mod to be sure.

[big stupid jellyfish]

Installing mods mid-playthrough it completely fine as long as it's not a large overhaul mod like Horizon or FROST. Uninstalling mods is more of an issue though.
Simple weapon and armor mods shouldn't cause any issues, but complex mods with lots of scripts will mess up your game if you remove them mid-playthrough.

[[IFC]Mjollnir]

Yup, faylen is right...simple replacers are usually nothing to worry about, but mods that use scripts to function normally get "baked" into your savegame, so even when you've uninstalled said mod but are using the savegame, the game tries to call those scripts which aren't there anymore, which can lead to instability and crashes...-can- lead to them, not neccessary 100% but still...
I'd advise to read through all installation instructions the mod author provides and also check the comments section of the mod (assuming you get it from the Nexus) if there are any problems reported..