Using the API to change a single property in a build step

Hi, I need to change the Octopus url in most of our TeamCity projects. I have written a simple app that has pulled-down all the info I need to find the affected build steps. The only thing I'm not sure about is whether I can update a single property, or if I have to supply all the properties in the PUT request.

https://teamcity-support.jetbrains.com/hc/en-us/community/posts/206838385-How-can-I-change-a-build-configuration-step-through-the-API-?input_string=Using%20the%20API%20to%20change%20a%20single%20build%20step%20in%20all%20projects doesn't address this, but implies that all properties are needed in the PUT request, even if they haven't changed

Thanks