Shinkansen luggage fee

In May 2020 I'll be going from Kagoshima to Nagoya. I have a large suitcase (155-160) which is just under the 160cm rule. I've done this before in the Green Car and put it behind the last row. With the new rule I bring it up when reserving my seat and they measure it there in the ticket office and get the ok? Or are there not much details on implementing yet? I'll be in Green Car.

If it is below 160 cm, no special arrangements are required. However, the space behind the last row of seats will be reserved for people sitting in the last row of seats. So, if you want to use it, you have to reserve a seat in the last row.

By the way, the space behind seats in Green Cars is blocked by foot rests and it is difficult to use:
http://m5hk.com/wp-content/uploads/2017/05/slproImg_201705220617462.jp...

These stupid foot rests also hinder tall people to stretch their legs when sitting.

My concern is that because it is so close to the limit it could be mistaken for over 160. When I made seat reservations on my last trip I mentioned last row because I have luggage and they would give me a seat in the last row.
My luggage ends up tilted against the back wall with the footrests. Maybe they will have a tag or sticker that get added to the bag to show it's been cleared.

and they measure it there in the ticket office and get the ok?
Given how many people never go to a ticket office to buy tickets, there will not be a measurement done when buying tickets. Plus, the layout in a ticket office would not facilitate taking measurements anyway.

If it is not over 160 cm, then it is not over 160 cm and the staff won't cause you troubles.