Insert letter or number with crunch -t flag
Thanks to Kamil Maciorowski for his answer.
When you use the character sets in crunch, it doesn't actually check if they're lowercase, uppercase, etc. It just checks which group it's in.
For example, if you have a4 e3 as your character set, you can have the -t field -t @w,som,, and it would fill the @'s with characters from the first group (a or 4), the ,'s with characters from the second group (e or 3), and so on.
So, I could use the command crunch 16 16 e3 i1 -t @v@ryth,ng,smin@ to find out what the password is.