Would it be ok to get a tab from another tab site, and fix it then submit it here?
I guess so but technically its not your Tab.
but you can write that its not yours that you only fixed it so i don´t think there would be a problem
Yes, there would be a problem; It's considered stealing. You can't take a take a tab, change a couple notes and submit it as your own. Tab the whole song yourself, mm'kay?