Can I make changes to the wiki?
Yes, absolutely.
You need editing permission before you can make changes to existing wiki pages (new pages can only be created by admin staff). Send your (preferably GMail*) email address and a quick note that you'd like to edit the WP KO wiki via the Contact links to the left (send to both as this gives you a better chance of getting a quick response).
Don't worry, your bank account won't be emptied and you won't receive unsolicited e-mails promising body part enhancements or untold riches from Nigerian royals.
All wiki edits are logged automatically. Changes can be undone, so don't be afraid to have a go as the more people involved, the better this resource will become.
*You can use a non-Google/GMail address, but you'll be asked to link this to a Google account (for verification). If you don't already have a Google account, you'll need to create one, so you might as well sign-in with this. The Google mail requirement is because the wiki is a Google (hosted) site.
How do I add a set to a manufacturer list?
How do I add a column to a manufacturer list?
If you feel that another column for piece count, series, etc. is warranted for a list, you can easily add it.
Just remember that you need to fill it in for all sets in the list.
How do I add a category to the Category column?
If the list doesn't contain an appropriate category for one or more sets, you can add it.
I buggered up a list entry. How do I fix it?
Pretty simple. Just click the name of the entry you want to correct in the Set Name column and the Add item dialog will open. Make your changes, then click Save.