I have an upcoming appointment with a massage therapist (12 years' experience) who is also a recent graduate of osteopathic college (an additional 5 years' training). He works at a local sports physio clinic that was recommended to me. There is a more experienced osteopath I would like to see, but she's about an hour's drive away (her colleague suggested the local physic clinic as an alternative). So for now I'm going with the local guy.

Essentially, what I'm hoping for is an assessment and/or gentle treatment of my neck/shoulders/spine area. I'm not having any major issues - at least, that I'm aware of or that my neuro has diagnosed - but the relative inactivity over the last year, possibly coupled with the nature of my injury (very solid blow to the top of my head), has resulted in some mild stiffness in that region.

Any suggestions as to how I might make the most of this appointment, and avoid overdoing it?

If it was my body, I would not let an osteopath try to manipulate my skull plates. His treatments of your neck and back should not cause pain. Muscle work may be painful and not damaging. I would be cautious about Deep tissue work.

I've seen an osteopath for work on my scull plates without problems, but I was lucky in that he was very experienced, and happened to have done his thesis on sports related concussions. It's typically called craniosacral therapy. I would just be cautious with the message therapist, as Mark said it shouldn't hurt, and they shouldn't work with too much pressure, which I think most message therapist tend to do so. Hopefully he'll be working on you from his osteopath capacity. With a lot of these alternative therapies, it really depends on the individual therapist.
My aunt also did some work on me, she's a physio with lots of extra training. She said she felt like like my scull was 'stuck' and had lots of 'blocked energy', so it's just very gentle and slow movements, and into the jaw and neck as well. It might help as you have that specific spot at the top of your head. The scull isn't fused into one solid piece, so it should have some movement in it.
It only helped me a tiny bit with my headaches, but it did help with my neck and upper back pain.

My daughter is a licensed massage therapist in California, and is currently taking advanced training including cranial sacral massage therapy, so I will ask her opinion. It’s somewhat controversial and isn’t generally considered a medical procedure. That said I find regular massage therapy helpful for both residual physical symptoms (upper back primarily), and it also helps me emotionally through reducing stress and aiding in my mindfulness practice.

So, I went to my appointment today. The therapist did an assessment, then I lay on my back and the therapist worked mainly on my neck and shoulders area. The treatment was firm but relatively gentle.

He said that my C5, C1 and C2 vertebrae were slightly rotated out of position. He did a gentle (non-aggressive) "functional" repositioning of C5 during the treatment. The rest of the time he worked on the surrounding neck and shoulder area. He said it felt like there was some possible scar tissue around C5 along with some fairly tense areas. I requested that he not attempt any cranial-sacral repositioning of the skull plates (not sure if he would have done this anyway).

Depending how I respond, he will take another look at C5 and possibly address the other two vertebrae during future treatments (just depends what I'm up for), along with general massage therapy. He did not think any aggressive treatment would be required to do this repositioning of the vertebrae. He generally recommends appointments every 2-3 weeks to allow the body to gradually respond to each treatment.

My neck felt slightly "worked" after the treatment but fine overall. No obvious negative effects. I feel pretty good about having attended at the clinic (10-min cab ride each way) and having undergone the treatment with no apparent problems.

Any thoughts or suggestions? Does this sound like a reasonable approach to massage therapy / osteopathic treatment?

Sounds like you found a great therapist! Sometimes just the effort of going to the appointment itself can be a lot, glad to hear you made it through. It's good of him to base the timing of the appointments based on how you feel. If you're not having any trouble after then, going more often would probably be more effective, if you can afford it. I was fortunate to have my parents chip in for part of my physio. Also, any work on your skull shouldn't be invasive, or involve any repositioning, it should be just to just to relieve pressure if anything is tight, just like anywhere else in your body. That's crazy about your vertebrae being out of position... I hope this brings you some relief!

greenfrog, I was thinking of seeing an osteopath as well, but my neck is so sensitive even a light massage gets me more dizzy / woozy. Is this one of your symptoms?