The simplest rifle that you can work on yourself is a Savage 10/110 series or any of the other variations.
All you need is an Action wrench and a Barrel Nut wrench.If you change calibers that don't have the same style case head,you'll also need to change the bolt head.
Savage rifle's are just an adult lego set,and pretty simple to work on if you have the tools and knowledge.
If changing a barrel,you will also need some Go/No Go gauges.
I just changed the trigger/barrel/barrel lug/barrel nut/bolt handle/scope base on my 110FLP-300 WM Tactical rifle today in a couple hrs.
Most other brands,require a gunsmith on a barrel change.