Lockdown Code updated for Gen 7. Credits to AWailOfATail and me (If you notice any bugs, please lmk)

lockdown.txt

/****************************************
			config/formats.js
****************************************/
	{
		name: "[Gen 7] Lockdown",
		desc: [
			"&bullet; <a href=\"http://www.smogon.com/forums/threads/3593815\">Lockdown</a>",
			"At the end of Turn 6, battlefield changes become permanent.",
		],
		section: "New Other Metagames",
		mod: 'lockdown',
		ruleset: ['[Gen 7] OU'],
		banlist: ['Damp Rock', 'Heat Rock', 'Smooth Rock', 'Icy Rock', 'Terrain Extender'],
		unbanlist: ['Genesect'],
		onBegin: function() {
			this.lockdownMoves = ['sunnyday', 'raindance', 'hail', 'sandstorm', 'magicroom', 'wonderroom', 'trickroom', 'gravity', 'electricterrain', 'mistyterrain', 'grassyterrain', 'psychicterrain', 'mudsport', 'watersport'];
			this.lockdownHazards = ['stealthrock', 'spikes', 'toxicspikes', 'stickyweb'];
		},
		onTryHitSide: function(target, source, move) {
			if (this.lockdownHazards.indexOf(move.id) > -1 && this.turn > 6) return false;
		},
		onTryHitField: function(target, source, move) {
			if (this.lockdownMoves.indexOf(move.id) > -1 && this.turn > 6) return false;
		},
		onResidualOrder: 999,
		onResidual: function () {
			if(this.turn !== 6) return;
			let pseudo = ['magicroom', 'wonderroom', 'trickroom', 'gravity', 'mudsport', 'watersport'];
			this.add("-message", "The Lockdown has commenced! Battlefield changes are now permanent!");
			if(this.weatherData.duration) this.weatherData.duration = 0;
			if(this.terrainData.duration) this.terrainData.duration = 0;
			for(let i in this.pseudoWeather) {
				if(pseudo.includes(i)) {
					this.pseudoWeather[i].duration = 0;
				}
			}
		},
	},

/****************************************
			mods/lockdown/scripts.js
****************************************/
"use strict";

exports.BattleScripts = {
	removeSideCondition: function(status) {
		status = this.battle.getEffect(status);
		if (!this.sideConditions[status.id]) return false;
		if(this.turn > 6 && this.lockdownHazards.includes(status.id)) return false;
		this.battle.singleEvent('End', status, this.sideConditions[status.id], this);
		delete this.sideConditions[status.id];
		return true;
	},
	setTerrain(status, source, sourceEffect) {
		status = this.getEffect(status);
		if(this.lockdownMoves.includes(status.id) && this.turn > 6) return false;
		if (sourceEffect === undefined && this.effect) sourceEffect = this.effect;
		if (source === undefined && this.event && this.event.target) source = this.event.target;

		if (this.terrain === status.id) return false;
		if (this.terrain && !status.id) {
			let oldstatus = this.getTerrain();
			this.singleEvent('End', oldstatus, this.terrainData, this);
		}
		let prevTerrain = this.terrain;
		let prevTerrainData = this.terrainData;
		this.terrain = status.id;
		this.terrainData = {id: status.id};
		if (source) {
			this.terrainData.source = source;
			this.terrainData.sourcePosition = source.position;
		}
		if (status.duration) {
			this.terrainData.duration = status.duration;
		}
		if (status.durationCallback) {
			this.terrainData.duration = status.durationCallback.call(this, source, sourceEffect);
		}
		if (!this.singleEvent('Start', status, this.terrainData, this, source, sourceEffect)) {
			this.terrain = prevTerrain;
			this.terrainData = prevTerrainData;
			return false;
		}
		return true;
	},
	setWeather(status, source, sourceEffect) {
		status = this.getEffect(status);
		if(this.lockdownMoves.includes(status.id) && this.turn > 6) return false;
		if (sourceEffect === undefined && this.effect) sourceEffect = this.effect;
		if (source === undefined && this.event && this.event.target) source = this.event.target;

		if (this.weather === status.id) {
			if (sourceEffect && sourceEffect.effectType === 'Ability') {
				if (this.gen > 5 || this.weatherData.duration === 0) {
					return false;
				}
			} else if (this.gen > 2 || status.id === 'sandstorm') {
				return false;
			}
		}
		if (status.id) {
			let result = this.runEvent('SetWeather', source, source, status);
			if (!result) {
				if (result === false) {
					if (sourceEffect && sourceEffect.weather) {
						this.add('-fail', source, sourceEffect, '[from]: ' + this.weather);
					} else if (sourceEffect && sourceEffect.effectType === 'Ability') {
						this.add('-ability', source, sourceEffect, '[from] ' + this.weather, '[fail]');
					}
				}
				return null;
			}
		}
		if (this.weather && !status.id) {
			let oldstatus = this.getWeather();
			this.singleEvent('End', oldstatus, this.weatherData, this);
		}
		let prevWeather = this.weather;
		let prevWeatherData = this.weatherData;
		this.weather = status.id;
		this.weatherData = {id: status.id};
		if (source) {
			this.weatherData.source = source;
			this.weatherData.sourcePosition = source.position;
		}
		if (status.duration) {
			this.weatherData.duration = status.duration;
		}
		if (status.durationCallback) {
			this.weatherData.duration = status.durationCallback.call(this, source, sourceEffect);
		}
		if (!this.singleEvent('Start', status, this.weatherData, this, source, sourceEffect)) {
			this.weather = prevWeather;
			this.weatherData = prevWeatherData;
			return false;
		}
		return true;
	},
};

Updated code with a shorter one