Adding an x to the end of the line of a file.

[Alcanjp]

Have a read here: https://hashcat.net/wiki/doku.php?id=rule_based_attack
TLDR; Create your own rule file with the two lines
$x
$X

and specify it in your command with the -r Parameter.

I previously asked where that file needed to be located".rule" and got no answer and therefor I thought it was not necessary.