Okay, so I already have an infection, but I wanted to change because I don't really like to one I have. Can I cure myself and change my infection and still be able to go along with the plot?

Please and thanks!

As far as I've seen you still can, but just so it's clear, your infection WILL start over from the base point, whichever one you get, and you therefore will NOT be able to access the Underground, Pastry Deliveries, or the Zombie Den until you're an "adult" zombie again. Did you get the Harlequin one or something?

Yes, you can cure yourself with the Extract of Loveberry potion. It sells for 69000 sp in the user shops.