I wouldn't add a comedic character whose 'job' it is to be 'the funny one'. Oh zappers no, that will not end well
If you just want to add humor to your story, it's also limiting if all the humour comes from one character, when some of the best humour that really catches your audience off guard tend to naturally arise from your existing characters and situations.
e.g. a number of jokes I plan on including in my comic bitwam will rely on callbacks to previous stuff that's happened (not necessarily running gags or brick jokes, since the original situation isn't always humourous (or intended to be a humourous setup), just referenced in a humourous way in a later scene). (My current jokes on the other hands mostly rely on real life references/memes, which isn't fitting for all stories XD)
I guess that's another reason why I'm not a pantser; when I already have some future scenes in mind, it gives time for my brain to come up with jokes relevant to that scene
Basically when I've been thinking about and spending time with my characters in my head for long enough, funni jokes/scenes/quips etc just tend to pop up and I just write them down whenever they do (even if I haven't nailed down where to place them, if I end up including them at all :P)