yes you can convert it to a StationXML, but it is a bit of manual work. Have a look at this tutorial here:
You’ll have to replace the response from NRL with a custom one. It might be helpful to start with an NRL one and inspect the required objects. If you assemble all the objects correctly, ObsPy can write it out as a StationXML file.
Yes - as I’ve written below I’d start with the link I’ve pasted in the previous answer. This gives you fully formed response objects. Use this to inspect how the objects are built-up and then replace values with your own. I think this is a good way of learning how our internal objects work. Alternatively you could of course also write out the StationXML file and edit it, or directly manually create a Response object with all its stages but this is tedious and fairly error prone.