[How to replace models of certain parts in a mod?]

I want to replace certain parts from USI-LS mod with my own models I designed. How should i do it?

[How should I install Principia for 1.7.1]

I am just dumb. 

Direct link from github: 1.5.1 - 1.7.3,

1.8.1 - 1.9.1

[[WIP][1.8.1, 1.9.1, 1.10.1, 1.11.0–2, 1.12.2–5] Principia—version ‎‎¹ki-din-nu, released 2024-05-08—n-Body and Extended Body Gravitation]

I want to install Principia, but I can't figure it out. Yes, I looked on Github, but it just doesn't work for me. I play on 1.7.1 and I am too lazy to reinstall all mods, so I'm sticking with that version. I am completely confused from the C++ too, because I am an amateur Java dev.

 

Edit: nvm I am just dumb.

[How should I install Principia for 1.7.1]

I am not new, I just can't remember password to my account. OK, I will ask there

[How should I install Principia for 1.7.1]

I am trying hard to install Principia for 1.7.1.  But I can't figure it out. Why 1.7.1? Because I do not want to reinstall all my mods again.

Thanks for Response.