This mod has its own input functionality. To change the input key for a function specific to this mod, open keyconfig.ini. In this file, simply set the values equal to the numbers of the keys you want. For instance, if you want player one's secondary fire key to be 'A', then you would do

PlayerOneSecondaryFire = 1

Below is a list of keystrokes with their corresponding numbers.

A - 1
B - 2
C - 3
D - 4
E - 5
F - 6
G - 7
H - 8
I - 9
J - 10
K - 11
L - 12
M - 13
N - 14
O - 15
P - 16
Q - 17
R - 18
S - 19
T - 20
U - 21
V - 22
W - 23
X - 24
Y - 25
Z - 26
0 - 27
1 - 28
2 - 29
3 - 30
4 - 31
5 - 32
6 - 33
7 - 34
8 - 35
9 - 36
Numpad 0 - 37
Numpad 1 - 38
Numpad 2 - 39
Numpad 3 - 40
Numpad 4 - 41
Numpad 5 - 42
Numpad 6 - 43
Numpad 7 - 44
Numpad 8 - 45
Numpad 9 - 46
- - 61
= - 62
{ - 65
} - 66
" - 69
\ - 70
, - 72
. - 73
ins - 76
del - 77
home - 78
end - 79
page up - 80
page down - 81
left arrow - 82
right arrow - 83
up arrow - 84
down arrow - 85
numpad / - 86
numpad * - 87
numpad - - 88
numpad + - 89
numpad . - 90
; - 105