OK, I went into the Template Modifications Manager.
Selected Add Template Modifation from the Default Style dropdown and clicked Go.
On that form, the
Product is set to vBulletin by default. Left it as it was.
The template I want to modify is navbarheader, so I selected that from the Template dropdown.
Gave it a title and a varname.
Now I don't really know what search and replace is for. Just want to paste some stuff in the template.
Didn't know what else to do at that point, so clicked Save.
Error appears:
Please select the processing mode. No idea what is. I don't see anything on the form that says "Processing mode" and wouldn't know what to select if it did.
So what am I doing wrong? ... and tell me again how straightforward this is?

I'm convinced this is worth figuring out but it's apparently gonna take some figuring.