Kieth, let's assume that your's is a statutory association and closely follows the requirements of the Private Ways Act (Title 23 Sections 3101-3104).  In that case you need to look to both the Act and your bylaws for guidance and then perhaps look to the courts to see how these issues have been settled in the past. I will admit that the answer to your question is not crystal clear.  

The bylaws section you quoted seems straight forward and on the surface it would appear that to change the method of assessment would also require a change in the bylaws.   So look to your bylaws to determine how they can be changed.  Usually bylaws changes require a some sort of super majority vote, say 66% or 75% approval.  The annual assessment, however, may only require a simple majority approval of above 50%.  But does that also change the allocation of the assessment?

Take a look at the statute.  Section 3101.5 reads in part "By a majority vote of the owners present and voting in person or by written proxy or absentee ballot, the owners may determine what repairs and maintenance are necessary and the materials to be furnished or amount of money to be paid by each owner for repairs and maintenance and may determine the amount of money to be paid by each owner for other costs, including, but not limited to, the cost of liability insurance for the officers, directors and owners and costs of administration. The determination of each owner's share of the total cost must be fair and equitable and based upon a formula provided for in the road association's bylaws or adopted by the owners at a meeting called and conducted pursuant to this section."(emphasis added.)

Based upon a formula provided for in the bylaw or adopted at a meeting?Does the statute override the bylaws? (usually statutes prevail) Can a simple majority vote change the assessment allocation?  Is the allocation you presented actually "fair and equitable"?  If the intent is to shift the cost burden to a different class of owner it may not be.  The courts seem to consistently give owners the right to determine their own fate regarding assessment allocation as long as fair and equitable prevails so a lot may hinge on that concept.  But there may also be an overriding legal concept on the sanctity of bylaws and for that you should seek a clear legal opinion before proceeding.  

So, in my opinion the answer to your question is not crystal clear but your prudent course of action is: change the bylaws or seek a legal opinion before moving forward.    

As stated in the other posts it is important to know what is required to make changes in the bylaws.  Yes, you can set up different rates based on criteria.  I was involved in setting up a Statutory Association in which we had a different rate for unimproved lots, no buildings.  They were charged 10% of the assessment amount of all the other lots. Seasonal people were charged the same as full time residents since it was their choice not to be there all year. If they did want to come up off season they benefited from the road being plowed so they could reach their property.  In addition access for emergency vehicles was possible in case something happened on their property.
Another association nearby paid by a share system.  People that exited the road a short distance in paid one share amount.  All others paid for two shares if they traveled farther down the road.  The system was actually challenged in court and the ruling was in the associations favor. The ruling from what I remember was the method was established and had been applied to everyone fairly.