As I understand it, anything done structurally or cosmetically to the building has to be in keeping, sympathetically undertaken and effectively not change it architecturally.
You retain the character or can return it to a more original condition. And ought to maintain it appropriately. Hence the Virginia creeper was doomed.
Once listed grade 1 (highest with most restrictions) or 2 there are statute laws to be obeyed.
But there may be even more rules e.g. in one case/area I know about, a committee had to be consulted.
You can't replace victorian patterned wood parquet flooring with practical industrial hospital type lino. It will have to be new same parquet that costs a fortune and takes weeks to lay, as happened in the Library in the same building with the v creeper on the outside wall.
Of course H&S and Equality means you can, with permission, install new lifts (elevators) and ramps.
You probably have something similar in the US.