Warnings themselves do not technically stack. They are just there to let you know you have broken a rule and that breaking that rule again in the future will result in an actual punishment. Having a warning on your account will not extend the punishment duration at all, punishment lengths are determined by your previous punishments of the same type. You can have multiple warnings for different things, but since they aren’t actually a punishment track, they won’t affect your play (like mentioned before).
Warnings only display in chat for 30 days, but remain on your account permanently, meaning if you got warned for swearing 2 years ago, if you swore again today, you would be muted without warning since you had that on your account in the past.
There is no way to appeal a warning since they do not limit your play at all and just serve as a warning. If the warning was false, it can be undone by talking to either Tacosbefriends (staff manager), or asking a moderator to forward you to the staff member who gave you the warning so you can ask them yourselves.
Hopefully this answered everything, and if you have any further questions, feel free to start a private conversation with me, or any other staff member. :)
~Locked