As long as you're adding relevant information to your ad, you're not breaking the rules. Adding location, adding photos, reducing the price, etc. are allowed. But posting in the thread just to bump it to the top will get either the bump or the whole thread deleted, depending on the severity of the violation.
The edit button for a post is disabled after a certain length of time, maybe a day or two IIRC.
Welcome to TheDieselStop