Can the lateral sides of the nasal bone be shaved down? By how many millimetres is possible?

Hello and thank you for your question.  The
best advice you can receive is from an in-person consultation.  It truly depends on how wide your mid-nasal vault is.  I agree with your goals of a harmonious appearance of the nose.  This is very important in rhinoplasty surgery.  Make sure you specifically look
at before and after pictures of real patients who have had this surgery
performed by your surgeon and evaluate their results.   The most
important aspect is to find a surgeon you are comfortable with. I recommend
that you seek consultation with a qualified board-certified plastic surgeon who
can evaluate you in person.
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

Lateral rasping is non-state-of-the-art and needless to say is a reckles, banned, unacceptable and disastrous maneuver; nasal bones are not thick blocks of marble, they are very suble paper-thick frames of bone which have to be very gently handled avoiding hollow depressions or random fractures.
There is no ground for your refusal to osteotomies, they are golden standards, a must and a required maneuver in every nasal work affecting the pyramid; not doing them leads to catastrophic complications and very complex revisions, like open roof deformity, broad dorsums, broad noses, inverted V lines deformity and pinched middle vaults with hourglass noses, all that together just for failing to perform osteotomies; dear Sir, you are deeply wrong, do refrain yourself to seek a surgeon who is "pliable" to your requirements, because sooner or later you'll find him... either due to his limited skills or just for money. Read my timeline of Q&A and you'll read hundreds of catastrophic results due to failed or absend osteotomies; you will not see ONE SINGLE case with negative consequences of well planned and properly executed osteotomies; you are conducting yourself based on obsessions, phobias or subjective ascientific criteria, which is a very dangerous way.
If you have a dorsal hump then it will need decapitation, shaving and reduction, leading to broad dorsum and open roof, which has to be closed with osteotomies, leading then to narrow, well defined and closed dorsum, narrow nasal base and narrow but not pinched middle vault.May you have a hump-less dorsum but broad, then the technique to fix this is way more sophisticated and challenging (most surgeons would leave a saddle nose deformity in these cases), by means of paramedial reduction of the synostosis (bone fusion) between nasal bones and bony septum made with manual Josephs saw, and the paramedial resection of the synchondrosis (cartilage fusion) betwetn upper lateral cartilages and the cartilagenous soft septum made by blade and scalpel; a fine and ellegant maneuver of high end skilled surgeons. Anyhow also leads a non-hump-shaving open roof and requires the osteotomies, there is no way around them.
Lateral rasping is unacceptable, before, now and ever, doing it you'd get crushing of nasal bones and a dramatic deformity of unimaginable magnittude.
If additionally you have issues at your tip, like bulbous, cleft, etc, then a complete open structure rhinoplasty is bound.
If you wish better grounded opinion well lit, focused and standard images have to be assessed: frontal, both lateral and both oblique views, also underneath the nostrils.
Feel free to request any additional information from me.