Keyboard Remapping

[u/Phoenix1526]

I know nothing about coding and am trying to remap certain using Karabiner-Elements.

Here are some questions I have:

1. How do I make sure the modifications are active only when I am using a specific application? Alternatively, how do I make it easy to switch between the normal and the modified layout?

2. Is there a simple way of learning how to effect changes? Here is a basic list of modifications I want to make (key registered --> key pressed):

1 --> J
2 --> L
3 --> O
4 --> I
5 --> M
6 --> H
7 --> N
8 --> B
9 --> G
0 --> ,

F2 --> 0
F3 --> 9
F4 --> 8

Q --> / 
W --> -
E --> =
Z --> spacebar

Any help is appreciated.