You can customize your instance by modifying the constants under the constant block in index.js. The code looks like this:

// ------------------- CONSTANT BLOCK EDIT IF RUNNING ON A CUSTOM SYSTEM ------------------
window.MAX_KNOWLEDGE_LEVEL = 4;
window.MAX_POINTS_ON_CHARACTER = 0.05;
window.ADD_POINTS_ON_ERROR_3_4 = 0.0375;            // 3/4 of 0.05
window.ADD_POINTS_ON_ERROR_1_2 = 0.025;             // 1/2 or 2/4 of 0.05
window.ADD_POINTS_ON_ERROR_1_4 = 0.0125;            // 1/4 of 0.05

window.CARD_WRITER_SIZE = 100;
window.CARD_WRITER_STROKE_ANIMATION_SPEED = 1.25;
window.CARD_WRITER_DELAY_BETWEEN_STROKES = 50;
window.CARD_DEFAULT_CHARACTER = "是"
window.CARD_DEFAULT_PREVIEW_NAME = "Preview Name"

window.WRITER_PADDING = 5;
window.WRITER_RADICAL_COLOUR = "#c87e74";
window.WRITER_SLEEP_AFTER_COMPLETE = 1200;          // In ms

window.WRITER_SHOW_HINT_ON_ERRORS = 3;
window.WRITER_SHOW_HINT_ON_ERRORS_LVL_3 = 1;

window.HOUR_UNIX = 36000000;
window.MINUTE_UNIX = 60000;
window.SECOND_UNIX = 1000;

window.CHARACTER_FETCH_URL = "https://cdn.jsdelivr.net/gh/MadLadSquad/hanzi-writer-data-youyin/data/";
// ---------------------------------- CONSTANT BLOCK END ----------------------------------

Do keep in mind, that messing with the grading settings may lead to some logical breakages in the application. Setting the grading level above 4, in particular, will simply increase the upper points limit but not change functionality in any way. Lowering it will disable advanced levels.