Can I edit, cancel, or withdraw a resource request that I created for a planned resource?

Yes. Click View Resource Request Details on the Manage Project Resources page to open the request, or select the request from the Manage Project Resource Requests page.

However, an error occurs if you already assigned a few resources, and then try to change the requested quantity to lesser than the assigned quantity. Also, you can't cancel or withdraw a request, if it has resources proposed, nominated, or assigned already.