I'm curious here ..............
There seems to be an assumption that limiting the MTOW is about reducing charges (as in landing fees?).......
However, airports charge landing fees according to generic weights of the a/c type (and series) ... not actual by registration...
Handling agents charge a fee plus per/kilo actual weight handled, normally.
The only cost reduction I'm aware of you achieve by declaring lower MTOW's is some maintenance items.......
I may, of course, have misunderstood ...........
ps .. edited to add: or do you mean NATS en-route charges