Walkthroughs for custom maps.

Maybe and can be done without plugins.

I tested every combination by trial from 100-255 in mapeditor years ago, the highest level you can lock is 868 by setting an experience limit of 109.

75 = 88; 89 = 100; 101 = 108; 109 = 868 [restriction = in-game effect]

In fact there are a few duplicates along the way but 109 was the earliest one and it didn't require special modifications for number positivity beyond cap of 127.
The only way to have a cap at 6424 is with a plugin because only caps of 0..255 are possible through mapeditor.