This project isn't maintained anymore by me. Feel free to fork it!
You want to scan a particular request of a web app, but there is a nasty parameter, which needs a different value on each request (e.g. different name for creating a file)? This extension could be a solution for your issue. It acts as session handling rule and replaces a defined token with a random value.
Define a session handling rule with a Burp extension action. Choose randomizer. Don't forget to set an appropriate scope of the session handling rule.
Send the request to the Repeater/Intruder and put #RANDOM# where randomization is required. Then send this request to the Scanner, Intruder or some different tool. The extension now replaces each occurence of #RANDOM# with a random token and #RANDOMNUM# with random number.
Placeholder, token length and character set can be set in a configuration section at the beginning of the script code.
WARNING: there seems to be a bug in Burp suite which causes that the request is truncated at the end when the placeholder length differs from the token length under certain conditions. Seems related to JSON requests, but could be something different. Keep lengths equal to stay safe!