Mmmmm.
Here is my two cents worth.
Because the bridge deck floor is being raised the roof needs to be raised too, causing all bulkheads and hull/cabin sides to be higher. Also consider storage and kitchen tops in the hulls. Longer daggerboards. This must add weight. Hull length remains the same and means this can make her look boxy . Tie-in from bridgedeck to hull angle will change
I am not convinced that this is a small change. You will find so many deviations from plan as you progress, that you may wish you never did.
Another issue is the boom height will be higher. Mast foot should now be 140mm higher? Forestay, and jib? Altered centre of effort?
Many builders have altered their bridgedeck clearance, but you never get any reports on satisfaction of outcome. You may have read that, that beautiful boat Lightwave (Gypsy) was lengthened. Once again no reports on performance.
I will always consult with the designer first. Notice also that Richard would have made Transit higher if 600mm was considered a problem on Eclipse. Roger Hill is another designer that does not subscribe to the 700-900mm clearance. This is providing your hull shape can take the boat over the wave and not through.
Regards
John H