In terms of difficulty, replacing a three-way electrical switch is a simple affair, so long as you adhere to safety protocols and follow the guidance on the back of the switch in regards to what wire goes where.
Once the power is out for that switch (or your entire dwelling if you want to be really safe,) the total time on this project is about 20 minutes at a maximum.
While more complex projects demand you hire a certified electrician, replacing a three-way switch is one you can do yourself if you want to save money or if there is no electrician to be easily had (say in a hunting camp.)
The important thing, besides following directions is to make sure you follow the guidance on the back of the switch. If you do that, you will have a replaced switch and working lights in no time!
Or electrician…
If you can’t change a plug, just wait and die in the dark
Replacing a 3-way switch doesn’t seem very SHTF prepping material.
“Awww man! First the world ends and now my 3-way switch doesn’t work! This week just keeps getting worse and worse!”
If you can’t match color coded wires to screws maybe you should be messing with any kind of switches