My neurosurgeon employed nerve monitoring and I received 'markers' prior to my surgery.
They indicate where a nurse (or whoever does the job) is to shave very small
'patches' to accommodate the nerve-monitoring electrode connections. The shaving was done 24 hours prior to the surgery, at a local hospital. I wore a baseball cap to the hospital on the day of my surgery. If you're having nerve monitoring, which I highly recommend, not to worry, the 'shaved patches grew back quickly. If you have long hair, they shouldn't even be noticeable. Ask your surgeon about the reason for the markers. If they are related to nerve monitoring during surgery, that's a good thing.
I couldn't shampoo for four days following my surgery. I hated it, even though I'm a guy. Hey, no one likes oily, dirty hair!
No clue on 'dry shampoo' but Psssssst
has been around a long time and sounds like it'll do the job for you.
I think you're going to be just fine and on top of that, post-op, you'll have clean, soft hair.
Things are looking up!